Method and system for bisphenol a production using water

ABSTRACT

Methods/systems for making a relatively high-purity bisphenol A product from phenol and acetone. Controlled turbulence is used to form bisphenol A adduct solids having improved physical properties. Phenol is separated from the bisphenol A product while inhibiting decomposition of bisphenol A.

This application is a divisional of application Ser. No. 08/632,663filed Apr. 15, 1996, now U.S. Pat. No. 5,959,158.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to methods and systems forproducing relatively high-purity bisphenol A products. Moreparticularly, in one embodiment of the invention, the methods andsystems relate to making a bisphenol A product of at least 99 weightpercent purity that is formed while decomposition of bisphenol A isinhibited. In another embodiment, the methods and systems relate toforming adduct solids that contain bisphenol A and have a length towidth ratio of less than about 5:1. Either one of the embodiments may beused in conjunction with the other embodiment.

2. Description of the Related Art

Bisphenol A ("BPA") is an important raw material in the production ofepoxy resins and polycarbonate resins. Bisphenol A may be produced byvarious techniques, but typically it is prepared in an acid-catalyzed,condensation reaction of two moles of phenol and one mole of acetone.Commonly-used catalysts include hydrochloric acid, a mixture of sulfuricacid and hydrochloric acid, and an acidic form of an ion-exchange resin.A secondary catalyst may be employed to shift the reaction toward theproduction of the p,p isomer and away from the production of the o,pisomer and other impurities. In the following description, it is to beunderstood that the term "bisphenol A" or "BPA" refers to the p,p isomerand not the o,p isomer, as the o,p isomer is considered an impurity. ABPA product having a purity of less than about 99.5 percent is usuallyunsuitable for making polycarbonates.

It is well known to practitioners of the art that exposure of bisphenolA to a temperature approaching or exceeding its pure melting point(about 157° C.) may cause partial decomposition of bisphenol A to formphenol and impurities such as isopropenyl phenol. Isopropenyl phenol isa highly reactive species that polymerizes to form color body precursorsthat may be oxidized to become color bodies. Color bodies areundesirable species that increase the yellowness index of polycarbonateresins. The yellowness index is a measure of the clarity of the resin.The clarity of the resin increases as the yellowness index decreases.Temperature-induced decomposition of bisphenol A intensifies when themolar concentration of phenol is less than that of bisphenol A, with therate of decomposition increasing as the concentration of phenoldecreases relative to the concentration of bisphenol A. Thus, it isadvantageous to maintain the temperature below about 150° C. in anyprocess step where the numbers of moles of bisphenol A present isgreater than the number of moles of phenol present. Decomposition ofbisphenol A increases as the time that the bisphenol A is exposed to atemperature above its pure melt point increases. "Heat history" refersto the amount of time that the BPA-containing medium has been exposed totemperatures in excess of the pure BPA melting point while the number ofmoles of bisphenol A present is greater than the number of moles ofphenol present. Those skilled in the art recognize that the suitabilityof a bisphenol A product as a raw material to make polycarbonates andother selected materials is inversely related to its heat history. Asignificant heat history may render the bisphenol A product totallyunsuitable for making polycarbonates and selected other materials.

Additionally, exposure of bisphenol A to oxygen and/or acidic specieswill tend to catalyze decomposition of bisphenol A. Therefore, a goal ofpractitioners of the art is to minimize the entry of oxygen and acidicspecies into the process. Small amounts of acidic species and oxygen areinevitably present in the process stream. Practitioners of the art tendto encounter problems when employing a vacuum system in the purificationand/or recovery process, since such a system may promote air seepageinto process streams, thereby providing additional oxygen for theformation of color body impurities.

The alcohol color is commonly used as a measure of the tendency ofbisphenol A product used for making epoxy resins to increase the colorof the epoxy resins. As the alcohol color of a BPA product decreases,the tendency of the BPA product to increase the color of an epoxy resindecreases. BPA products having an alcohol color greater than about 20may be unsuitable as a raw material for some epoxy processes. Thecaustic color is commonly used as a measure of the tendency of bisphenolA product used for making polycarbonate resins to increase theyellowness index of the resins. As the caustic color of a BPA productdecreases, the tendency of the BPA product to increase the yellownessindex of a resin decreases. BPA products having a caustic color greaterthan about 15 tend to be unsuitable for making polycarbonates with lowyellowness indexes.

In the preparation of bisphenol A by the reaction of phenol and acetone,practitioners of the art typically perform an initial purification step(i.e., the first adduct crystallization step) in which an adduct solid(i.e., adduct crystal) is formed that has a substantially equal numberof moles of bisphenol A and phenol.

Some methods relate to recovering a bisphenol A product directly fromthe BPA-phenol adduct crystal without further intermediate purificationsteps. Bisphenol A product is then typically recovered. Often, thesemethods involve a second adduct crystallization to produce anintermediate grade product from the mother liquor (i.e., from the liquideffluent in the first adduct crystallization step) that failed tosolidify in the first adduct crystallization. The intermediate gradesolids are then typically recycled into the feed stream of the firstadduct crystallization zone to increase the bisphenol A concentration inthe feed stream and to increase the amount of bisphenol A relative toimpurities in the first adduct crystallization zone.

Some methods relate to melting the adduct crystal to form a melt, andthen stripping phenol from the melt in a falling film still or wipedfilm evaporator.

The-above-described methods typically operate under a vacuum at apressure of about 30-50 torr and expose bisphenol A to a temperature ofabout 180-200° C. Trace amounts of phenol are then removed by steamstripping at a temperature typically about 180-200° C., leaving abottoms product melt termed "crude bisphenol A." The crude bisphenol Ais then further purified in a medium other than phenol, with the mediumtypically being an organic solvent. Typically, the crude bisphenol A iscrystallized from the medium, and then the bisphenol A product istypically melted and subjected to a distillation procedure to removeresidual solvent from the melt before a bisphenol A product isrecovered.

Some methods relate to redissolving the adduct crystals in clean phenoland again extracting a bisphenol A adduct crystal in a secondcrystallization step. Phenol may then be removed using a falling filmstill or wiped film evaporator, and a steam stripper, at temperatures asdescribed above. The remaining finished bisphenol A is then solidifiedin a prilling or flaking process. Such prilling and flaking processesare well known in the art.

A variety of techniques exist for the recovery of a sufficiently purebisphenol A product for use in polycarbonates, however it is believedthat all such processes used by practitioners of the art exposebisphenol A to a temperature above at least 160° C.

Chang et al. (U.S. Pat. No. 4,533,764) appear to disclose a methoddirected to "removing the remaining small quantities of solvent to aparts per million level", the solvent being "occluded solvent" that ispresent in bisphenol A "produced from solvent crystallization." Chang etal. mention solvents including methanol, acetone, methyl formate,benzene, toluene, xylene, 2-propanol, chloroform, methylene chloride,ethylene dichloride, and trichloroethane, however phenol is not statedas a solvent applicable to the Chang et al. process.

Iimuro et al. (U.S. Pat. No. 4,931,146) appear to disclose a process forobtaining high-priority bisphenol A by removing phenol from an adduct ofbisphenol A with phenol and removing continuously the residual phenol bysteam stripping, wherein a multi-tubular packed column is used asstripping equipment. The method of Iimuro et al., however, appears tosubject bisphenol A to high temperatures (160-200° C.) during theremoval of phenol.

Jakob et al.(U.S. Pat. No. 5,269,887) appear to disclose a method inwhich phenol is removed from a BPA-phenol adduct using solid phasedrying (sublimation). The method of Jakob et al., however, employs avacuum. This vacuum tends to promote air seepage into the process. Agoal of practitioners of the art is to minimize oxygen exposure in thesystem to prevent the formation of color bodies.

A number of other patents appear to be directed at purifying bisphenolA, including U.S. Pat. No. 4,354,046, U.S. Pat. No. 3,673,262, U.S. Pat.No. 3,290,391, U.S. Pat. No. 3,219,549, U.S. Pat. No. 2,791,616, U.S.Pat. No. 3,326,986, U.S. Pat. No. 3,535,389, and U.S. Pat. No.5,475,152. It is believed that the solvent leaching techniques presentedin many of these references are typically performed subsequent to a hightemperature distillation step in which a crude bisphenol A product isobtained. Such leaching techniques alone are believed to be insufficientto produce a bisphenol A product of adequate purity for use inpolycarbonate resins.

All of the above-mentioned patents are herein incorporated by reference.

Adduct solids of bisphenol A have a natural tendency to grow in a long,slender shape. Practitioners of the art typically produce bisphenol Asolids with a length to width ratio of at least 5:1. In the preparationof adduct solids that contain bisphenol A, the formation of "short,""fat," robust solids with the lowest possible length to width ratio ispreferred to allow the formation of a stable and porous cake duringrecovery of the solids. As the porosity of the solids cake increases,the cake wash efficiency is increased and the deliquoring properties ofthe cake are enhanced. Practitioners of the art aim to create a gentleenvironment for solidification in order to prevent breakage of thesolids. In addition, a gentle environment avoids turbulence that mayinduce secondary nucleation. Secondary nucleation tends to result in theformation of "fines." "Fines" are relatively small (e.g., less than 20micron average width), undesirable solids that promote the formation ofa tight, compact cake with poor deliquoring and wash characteristics.Tight, compact cakes have a large surface area to volume ratio and tendto hold excessive amounts of liquor. Practitioners aim to create largersolids to inhibit compacting of the recovered solids cake. To achievethe formation of larger solids, practitioners of the art maintain a lowstream velocity in their crystallizers to prevent turbulence andbreakage of the formed solids. Additionally, some practitioners of theart remove acetone and water from the composition from which theBPA-phenol adduct solid is formed. Acetone and water are removed fromthe composition prior to its introduction into a solidification unitwhere the adduct solid is formed. An effect of the removal of acetoneand water is a significant increase in the viscosity of the composition,which impedes the formation of turbulence in the solidification unit.

SUMMARY OF THE INVENTION

One embodiment of the invention relates to making a bisphenol A productof greater than about 99 weight percent purity that is formed in aprocess where decomposition of the bisphenol A is inhibited. Phenol andacetone may be reacted, resulting in a reactor effluent that includesbisphenol A, phenol, unreacted acetone and water produced by thereaction. The effluent may be directed to a first solidification systemand then a first recovery system where a solid (e.g., adduct) ofbisphenol A and phenol is obtained. Water (e.g., liquid or steam) may beadded to the adduct to form an adduct solution with a lower meltingpoint than the adduct solid. The adduct solid may be melted before suchwater is added. Phenol may be removed from the adduct solution in acolumn at a temperature below about 150° C. to inhibit the decompositionof bisphenol A to color body precursors. The pressure of the column ispreferably greater than atmospheric to avoid air seepage into the systemthat may oxidize any color body precursors present in the system. Thecolumn bottoms stream preferably contains less than about 1 weightpercent phenol, and at least a portion of it is preferably directed tothe second solidification system and second recovery system where abisphenol A product is obtained that contains at least about 99 weightpercent bisphenol A.

Another embodiment of the invention relates to forming "solids" thatcontain bisphenol A and have a mean length to width ratio of less thanabout 5:1. It is to be understood that "solids" refers to useful, growthsolids such as crystals and the like. Phenol and acetone may be reacted,resulting in a reactor effluent that includes bisphenol A, phenol,unreacted acetone and water produced in the reaction. The effluent maybe passed through a solidification chamber. The turbulence of the streamin the chamber is preferably monitored. The turbulence of the stream isalso controlled to allow sufficiently turbulent flow to fragment firstsolids to initiate the formation of second solids having a length towidth ratio of less than about 5:1. The turbulence may also becontrolled to inhibit or prevent: (a) substantial secondary nucleationfrom being induced by the turbulence, (b) a fouling rate of a coolingsurface to exceed a specified rate, and/or (c) formation of fines. Aportion of the stream preferably exits the chamber into a recoverysystem where the solid product is preferably separated and washed. Theportion of the stream that is not recovered as a solid product ispreferably directed to a drying column where acetone and water areremoved. The drying column is preferably located downstream of the firstsolidification system so that the viscosity of the reactor effluent isnot increased prior to the introduction of the effluent into thesolidification chamber.

The above-mentioned embodiments may be used in combination with oneanother. In another embodiment, the above-mentioned improvedsolidification method may be employed to make the BPA-phenol adduct inthe above-mentioned method of making a bisphenol A product of at least apurity of 99 weight percent while inhibiting the decomposition ofbisphenol A.

An advantage of an embodiment of the invention is that it can be used tomake a bisphenol A product of at least 99 weight percent bisphenol Athat has no heat history.

Another advantage of the invention is that it may be used to reduce themelt point of a BPA-phenol adduct solid, allowing the removal of phenolin a column at a pressure of at least atmospheric pressure and at alower temperature than is possible in conventional processes.

Another advantage of the invention relates to improving the physicalproperties of bisphenol A adduct solids.

Yet another advantage of the invention relates to decreasing the rate offouling in a bisphenol A solidification system to improve productioncapacity of the system.

Still another advantage of the invention relates to maintaining afavorable stream viscosity to facilitate creation of a selected amountof controlled turbulence in a bisphenol A solidification system.

Another advantage of the invention relates to reducing the concentrationof trace acids and chlorides in an adduct solution with an anionicexchange resin.

Yet another advantage of the invention relates to substantiallyeliminating the presence of fines in a bisphenol A solidification unitwithout adding heat to the system.

Further advantages, and novel features are provided in the followingdetailed description and will become apparent to those skilled in theart.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram illustrating various embodiments of theinvention.

FIG. 1A depicts alternate embodiments of dryers.

FIG. 1B (a-c) depicts alternate embodiments of crystallizers in a secondsolidification system.

FIG. 1C (a-b) depicts alternate embodiments of first recovery system 40.

FIG. 2 is a schematic diagram of an embodiment of a solidificationsystem.

FIG. 3 is a schematic diagram of another embodiment of a solidificationsystem.

FIG. 4 is a schematic diagram of an embodiment of a column.

FIG. 5 is a schematic diagram of an embodiment of a pump.

FIG. 6 is a schematic diagram of another embodiment of a pump.

FIG. 7 is a plot of cumulative volume/weight for various solids(crystals) made in a plant in India.

DETAILED DESCRIPTION

This invention generally relates to methods, systems and apparatus formaking a relatively high purity bisphenol A product.

Referring to FIG. 1, in an embodiment, mixture 1 of phenol and acetoneis introduced into a reactor 10. Mixture 1 preferably may be at atemperature ranging from about 60° C. to about 65° C. Mixture 1 may beintroduced into a reactor system that includes more than one reactor 10,and the reactors may be arranged in parallel, series, or in paralleltrains, the trains including reactors connected in series.

Reactor 10 preferably contains an ion-exchange (e.g., cation) resincatalyst in the form of beads, although the reaction of phenol andacetone to produce bisphenol A may be accomplished by various othercatalysts well known in the art. Ion-exchange resin 13 may absorb asignificant amount of color bodies and other impurities. Water may alsobe absorbed by resin 13 causing it to swell and dump amounts of colorbodies and other impurities into the process stream. The amount of waterentering reactor 10 in mixture 1 is preferably minimized, since anadditional amount of water is formed during the reaction of phenol andacetone. In an embodiment, the mixture 1 preferably contains less than0.1 weight percent water. The reaction of phenol and acetone isexothermic, however reactor 10 is preferably operated so that the heatgenerated during the reaction causes the reactor effluent to emerge at atemperature below about 75° C. When reactor effluent 12 is at atemperature greater than about 75° C., cooler 11 may be required to coolthe effluent to allow effective operation of first solidification system20. In an embodiment, mixture 1 flows vertically through the reactor ina direction from the bottom of the reactor to the top of the reactor.Acetone is preferably maintained in slight stoichiometric excess ofbisphenol A formed in reactor 10 to inhibit the formation of additionalimpurities, thereby inhibiting a corresponding decrease in BPAformation. Reactor effluent 12 includes bisphenol A, phenol, andpreferably less than about 3 weight percent (and more preferably, lessthan about 1 weight percent) each of water and acetone.

Practitioners of the art typically purge at least a portion of heavyprocess impurities when they reach or exceed a predetermined level inreactor 10. The purge commonly is withdrawn from a stream that isrecycled to the reactors. In an embodiment of the invention, the levelof impurities is allowed to build until it reaches or exceeds anequilibrium level. The equilibrium impurity level is reached when about1 part of impurities is present for an amount of bisphenol A betweenabout 1.4 and 2.0 parts. While the level of impurities is at or inexcess of the equilibrium level, few or no new impurities will be formedin the reactor. The level of impurities may approach the equilibriumlevel if impurities rearrange to form BPA, and the level of impuritiesmay fall below the equilibrium level if impurities leave the process ina bisphenol A product. A relatively small amount of new impurities mayform to replace the impurities that have rearranged to form BPA or thathave exited the process in a BPA product. Ion-exchange resin 13 ispreferably capable of absorbing impurities for a substantial time periodbefore regeneration or replacement of the resin is necessary. In oneembodiment, the purging of impurities and replacement or regeneration ofthe ion-exchange resin each occur once per year of operation. Purgingless frequently than is done in conventional methods substantiallydecreases the mass of impurities formed, hence decreasing the mass ofimpurities that must be treated. Additionally, reducing the mass ofimpurities formed tends to increase the mass of product BPA that can beproduced per unit mass of mixture 1.

In an embodiment, reactor effluent 12 is directed to firstsolidification system 20. A number of embodiments of solidificationsystem 20 are illustrated in FIG. 2 and FIG. 3. Solidification system 20preferably includes a solidification chamber 21 within which stream 34is substantially continuously stirred, agitated, or circulated. In anembodiment, the solidification chamber includes a conduit loop. Such asolidification chamber (e.g., conduit loop) applicable to methods of thepresent invention is available from Messo-Chemietechnik in Duisburg,Germany. Within the solidification chamber is a solidification zone, aregion where solids may form in stream 34.

The solidification zone occurs where stream 34 is "supersaturated" withbisphenol A. "Supersaturation" of stream 34 with bisphenol A means thatan excess of bisphenol A is present in stream 34 such that not all ofthe bisphenol A present can dissolve in stream 34. Supersaturation alsogenerally means that the stream is below its "cloud point" with respectto bisphenol A. As the temperature of stream 34 is lowered, thesolubility of bisphenol A in the stream will decrease. The "cloud point"of a stream is the temperature at which the formation of solids in thestream may first be visually observed.

The formation of solids in stream 34 will cease without supersaturation.As such, the formation of solids in stream 34 will cease when an amountof bisphenol A solidifies and causes the concentration of bisphenol A inthe fluid phase to fall below a concentration range necessary forsupersaturation.

The formation of solids will also cease if the stream temperature risesabove the cloud point. Such a temperature rise may be due to heatgenerated by solidification and/or the inflow of feed at a temperatureabove the cloud point. In an embodiment, the solidification zoneincludes substantially all points where stream 34 is present insolidification chamber 21a. In an embodiment, solidification chamber 21bis of sufficient length to allow stream 34 to fall essentially to thelevel of bisphenol A saturation in the conduit loop at point 22, locatedimmediately before the feed enters first solidification system 20through feed conduit 28.

Practitioners of the art typically aim to maintain a concentration ofbisphenol A of below about 20 weight percent in the feed stream tosolidification system 20. In an embodiment of the invention, however,the feed stream to solidification system 20 includes about 30 weightpercent bisphenol A, about 50 weight percent phenol, and about 20 weightpercent impurities. Methods of the present invention allow the formationof a sufficient amount of solids having a desirable shape using the feedcompositions described above as well as many other feed compositions.

In an embodiment, cooling system 23b includes cooling surface 24b and isemployed within the solidification chamber to remove heat from thechamber such that the temperature of stream 34 within the solidificationzone is controlled within a predetermined range (i.e., between about 40°C. and about 55° C.). In an embodiment, cooling system 23b includes ashell and tube heat exchanger, and stream 34 preferably flows throughthe tubes 132 of the exchanger, with a cooling fluid flowing through theshell side. In an embodiment, solidification system 21a preferablyincludes a vessel 175 with a cooling surface 24a (located, e.g., oncooling coil 171) located within the vessel. In an embodiment,solidification system 21a includes a vessel with a cooling surface 24a(located, e.g., on cooling coil 176) located on the exterior of thevessel. In each of the above embodiments, the cooling fluid ispreferably water, although any of a number of cooling fluids may beused. A number of other cooling systems may be used withinsolidification system 20. Preferably stream 34 is maintained at atemperature above 40° C. to prevent freezing of phenol, which has a puremelt point at about 41° C.

Some practitioners remove a significant portion of the water and acetonein reactor effluent 12 prior to the entrance of the effluent intosolidification chamber 21. Removing water and acetone from the streamincreases the viscosity of the stream and decreases the solubility ofbisphenol A in effluent 12. Hence, solidification cooling requirementstend to be decreased.

In an embodiment of the invention, however, water and acetone preferablyremain in effluent 12 when it enters first solidification system 20.Bisphenol A is more soluble in effluent 12 prior to the removal of waterand acetone from the effluent. Therefore, the cloud point temperature ofeffluent 12 may be reduced by the water and acetone remaining ineffluent 12. Practitioners typically seek to minimize the amount ofcooling required for solidification, however additional cooling may berequired for solidification when acetone and water are allowed to remainin effluent 12. The presence of acetone and water in stream 34 reducesits viscosity, however, providing advantages as described below.

The turbulence of stream 34 is controlled as it passes through chamber21. A significant embodiment of the invention relates to achieving andcontrolling turbulence in stream 34 to reach a selected level ofturbulent flow that is sufficient to break or fragment a portion ofsolids in the stream. In an embodiment, driving system 141b controls thevelocity of stream 34 to create turbulence in the stream as it passesthrough chamber 21b. In an embodiment, turbulence is created andcontrolled in stream 34 as it passes through chamber 21a using drivingsystem 141a. Turbulence in stream 34 preferably occurs as the streamcontacts the cooling surface 24a/24b. In an embodiment, turbulence iscreated and controlled in stream 34 as it passes within the tubes 132 ofcooling system 23b. In another embodiment, turbulence is created andcontrolled in stream 34 as it passes over coil 171 in solidificationchamber 21a. In yet another embodiment, turbulence is created andcontrolled in stream 34 as it contacts cooling surface 24a of both coil171 and coil 176.

It is believed that creating and controlling turbulence in the mannerdescribed above is contrary to conventional wisdom. Practitionerstypically aim to prevent solids from fragmenting to allow the formationof larger solids. The method of the present invention, however, relatesto fragmenting a portion of the solids in chamber 21 known as "firstsolids." "First solids" are solids that have a tendency to fragment whensubjected to the controlled turbulence generated in chamber 21 due totheir relatively high length to width ratio (e.g., typically 6:1, 8:1,or greater). The relatively high length to width ratio imparts a lowbeam strength to first solids, making them susceptible to fracture in adirection parallel to their width. First solids are undesirable sincethey may fragment into smaller particles when subjected to thecentrifugal forces of conventional solid-liquid separators. As such,first solids promote collapsing of the recovered solids cake, resultingin a denser cake with diminished washing and deliquoring efficiencies.First solids may include relatively large solids and/or relatively smallsolids, since a key feature contributing to collapse of a recoveredsolids cake is the shape (e.g., length to width ratio) of the solidswithin the cake.

"Second solids" are solids that have a stronger tendency to resistfracture when subjected to the turbulence in chamber 21 due to theirrelatively low length to width ratio. In an embodiment, the velocityand/or agitation of stream 34 is adjusted to achieve a controlledturbulence such that the first solids fragment, while the second solidsremain intact. First solids may be repeatedly fragmented until secondsolids are produced from the fragments. The formed second solids mayfurther develop in chamber 21, with their maximum overall growth tendingto depend upon their width, since they will likely fracture if theirlength exceeds a certain multiple of their width.

The precise length to width ratio where fracture has a tendency to occurdepends upon a number of system factors discussed in the following. Theformation of an excessive amount of first solids at any time in chamber21 is preferably prevented by the constant maintenance of controlledturbulence within chamber 21, with the turbulence preferably occurringat least at locations proximate to cooling surface 24. In an embodiment,the turbulence within chamber 21 is controlled such that first solidshave a length to width ratio of greater than about 5:1 and second solidshave a length to width ratio of less than about 5:1. In a more preferredembodiment, the turbulence is controlled such that first solids have alength to width ratio of greater than about 3:1 and second solids have alength to width ratio of less than about 3:1. In a still more preferredembodiment, the turbulence is controlled such that first solids have alength to width ratio of greater than about 2:1, and second solids havea length to width ratio of less than about 2:1.

Increasing the level of controlled turbulence tends to increase heattransfer from stream 34 to cooling surfaces 24a/24b, thereby decreasingthe temperature difference between the cooling medium within coolingsystem 23a/23b and stream 34. The decreased temperature differencelessens the formation of solids on cooling surfaces 24a/24b, decreasingthe rate of "fouling" on the cooling surfaces and the frequency withwhich chamber 21a/21b must be shutdown to melt solids from the coolingsurfaces and/or walls of the chamber. "Fouling" is the depositing ofmaterial on a heat transfer surface. Such material tends to have a lowthermal conductivity and provides a resistance to heat transfer, therebylowering the efficiency of heat transfer to or from the heat transfersurface. When the level of fouling reaches a predetermined level, system20 must be shutdown to remove deposits from cooling surfaces 24a/24b.Such shutdowns decrease the annual production of chamber 21a/21b, hencea decrease in the fouling rate on cooling surfaces 24a/24b will increasethe production capacity of chamber 21a/21b.

In an embodiment, a system is adapted to determine the pressuredifferential at various time intervals between points in thesolidification zone. Such pressure differentials may be used to estimatethe rate of fouling on the cooling surfaces so that the turbulence ofstream 34 may be adjusted accordingly. The system may include any numberof pressure gauges well known in the art, and, optionally, aprogrammable computer connected via electronic lines to such gauges.

In an embodiment, a controlled level of turbulence is maintained toinhibit the fouling rate on cooling surface 24a such that chamber 21a isshutdown about once every 60 hours to remove deposits from the coolingsurface. Such a shutdown frequency is an improvement over similarconventional solidification chambers that must be shutdown about every 6hours. In an embodiment steam is passed through coil 171 and coil 176for about 30 minutes during shutdown of chamber 21a to remove depositsfrom cooling surface 24a. In an embodiment, the removed depositspreferably remain in chamber 21a and serve to initiate solids formationonce chamber 21a is restarted.

In an embodiment, a controlled level of turbulence is maintained toinhibit the fouling rate on cooling surface 24b such that chamber 21b isshutdown about once every 2-20 days to remove deposits from the coolingsurface. Different systems may be shutdown once every 3-5 or 6-10 days.In an embodiment, stream 34 is heated to a temperature below about 135°C. in chamber 21b for about 30-45 minutes to remove deposits fromcooling surface 24b. The exact temperature to which stream 34 is raisedshould be determined empirically. The temperature should not be raisedtoo high such that stream 34 circulates around chamber 21b due tothermal effects. The level of stream 34 within chamber 21b is preferablysufficiently low to prevent overflow of stream 34 through conduit 27 dueto expansion of the stream. The level of stream 34 within chamber 21b ispreferably sufficiently high to immerse tubes 132 in the stream toprevent the partial melting of the deposits on tubes 132. If thispartial melting occurs, phenol may be released from the deposits,leaving a pure bisphenol A deposit on tubes 132. The removal of a purebisphenol A deposit from tubes 132 would require the temperature ofstream 34 to be raised above about 157° C., tending to causedecomposition of the bisphenol A. In an embodiment, the removed depositspreferably remain in chamber 21b and serve to initiate solids formationonce chamber 21b is restarted.

In an embodiment, the temperature of stream 34 within chamber 21 isgradually reduced to about 60° C. to initiate the formation of solids.

In an embodiment, the temperature difference between stream 34 and thecooling medium that contacts cooling surfaces 24a/24b is monitored todetermine the fouling on cooling surfaces 24a/24b. The degree of foulingtends to be directly proportional to the increase in the temperaturedifference between stream 34 and the cooling medium for a selectedamount of heat transfer. Thus, the temperature difference between stream34 and the cooling medium that is required to cool stream 34 to aselected temperature will tend to increase over time as the degree offouling on cooling surfaces 24a/24b increases. In an embodiment, thecontrolled level of turbulence is adjusted as a function of thetemperature difference between the cooling medium and stream 34.

"Primary nucleation" is the formation of solids in a stream thatproceeds due to the supersaturation level of a stream. Primarynucleation is preferable because it allows the formation and growth ofsolids to occur in an orderly manner. At excessive levels of turbulence,"secondary nucleation" and/or "spontaneous nucleation" may be inducedand additional sites may become available for initiation of solidsformation. "Secondary nucleation" is the formation of solids due tostresses present in a supersaturated stream. Such stresses may includeshear stresses, impact stresses, and/or cavitation stresses. Secondarynucleation is undesirable because it promotes the formation of numerousfines, which provides additional sites and surface area for the growthof bisphenol A solids. The result is the development of solids at agreater number of smaller sites, which adversely affects the sizedistribution of the formed solids. The mean size of the solids will tendto decrease. "Spontaneous nucleation" is more severe than secondarynucleation and is characterized by the formation of an increased amountof fines, with most all of a dissolved solid (bisphenol A) contained inthe stream solidifying to form fines. Spontaneous nucleation may beinduced (a) by extreme levels of turbulence in a stream, (b) if thetemperature of the stream falls too far below its cloud point, (c) or acombination thereof. The turbulence and/or temperature of stream 34should be controlled to prevent inducement of significant secondarynucleation and/or spontaneous nucleation by the turbulence. In anembodiment, the velocity and/or agitation of stream 34 is controlled toattain as great a level of turbulence as possible without inducingsignificant secondary or spontaneous nucleation.

The optimum turbulence needed to achieve selected physical properties ofthe solids formed in stream 34 may vary among embodiments of theinvention. The optimum turbulence depends on various system factorsincluding: (1) the shape of solidification chamber 21, (2) thecharacteristics of any pumps or agitators used within solidificationchamber 21, (3) the composition and temperature of stream 34, (4) thedegree of supersaturation of bisphenol A in stream 34, (5) the viscosityof stream 34, and (6) the density of the formed solids. In anembodiment, the optimum turbulence is determined empirically in thefollowing manner. With the system at equilibrium, selected physicalproperties of the solids formed in stream 34 are determined using ananalyzer (e.g., analyzer 131). The physical properties that aredetermined using the analyzer preferably include the mean length towidth ratio of the formed solids and the mean width of the formedsolids. The analyzer also is preferably capable of revealing selectedphysical properties of individual solids, particularly the solids thathave the greatest or least values for any of the selected physicalproperties. The analyzer preferably is adapted to automaticallydetermine selected physical properties characteristics, however otherdevices adapted to analyze solids may be used as well. In oneembodiment, a magnifying means may be used to visually observe thesolids to determine physical properties of the solids. Upondetermination of the selected physical properties, the turbulence ofstream 34 is increased using a pump and/or agitator and/or other meansknown in the art. Screens, shakers, and/or weights may also be used.After the system has reached equilibrium, samples of the solids areanalyzed to determine selected physical properties, and the turbulencein the stream is again increased. Secondary and spontaneous nucleationmay be detected by analyzing the physical properties of solids. Anincrease in the presence of fines as the turbulence level increases islikely an indication of the presence of substantial secondary orspontaneous nucleation. After substantial secondary or spontaneousnucleation is detected, the turbulence of stream 34 is decreased to alevel such that substantial secondary nucleation ceases. The turbulenceshould be repeatedly adjusted as a function of the selected physicalproperties of stream 34 as determined by the analyzer. Ultimately, amaximum level of turbulence should be achieved such that substantialsecondary nucleation does not result from the turbulence. As thevelocity of stream 34 is increased, the flow of coolant in coolingsystem 23a/23b may have to be increased accordingly. In one embodiment,the optimum turbulence is achieved in a stream having a velocityexceeding 6 feet per second.

In an embodiment, pump 25b having impeller 26 (shown in FIG. 5) and avariable speed motor 140 is used to pass stream 34 throughsolidification chamber 21b. The velocity and/or agitation of stream 34is preferably controlled by adjusting the speed and/or size of impeller26. In an embodiment, the control system is used to vary the speed ofimpeller 26. The control system preferably includes analyzer 131, whichmay include a screening system to size various solids. Analyzer 131 isused to determine physical properties of the solids formed insolidification chamber 21. Control system 130a/130b is adapted to send asignal to the variable speed motor to vary the speed of impeller 26 as afunction of the physical properties of the solids. As the speed ofimpeller 26 increases, the flow rate and velocity of the stream areincreased, thereby increasing the level of turbulence in the streamwithin solidification chamber 21. Control system 130a/130b may be usedto continuously adjust the turbulence of stream 34 to attain preferredphysical properties of the solids formed in the stream.

In an embodiment, pump 25 includes a chamber 190 and a piston 191 with avariable stroke length. The control system may be used to vary thestroke length. Analyzer 131 is used in the manner described above todetermine the physical properties of the solids formed in solidificationchamber 21. Control system 130a/130b is preferably adapted to send asignal to pump 25 to vary the stroke length as a function of thephysical properties of the solids. As the stroke length increases, theflow rate and velocity of the stream are increased, thereby increasingthe level of turbulence in the stream throughout solidification chamber21. Control system 130a/130b may be used to continuously adjust theturbulence of stream 34 to attain preferred physical properties ofsolids formed in the stream.

In an embodiment, agitator 172 is used to create a selected level ofturbulence in stream 34. Agitator 172 preferably includes a blade 173,but any agitating system well known in the art may be used. Agitator 172may be the sole means by which the selected level of turbulence iscreated or it may be used in conjunction with other systems includingpumps as described above. In one embodiment, the agitator includes avariable speed motor 174 and control system 130a that adjusts the speedof a blade 173 on agitator 172 as a function of selected physicalproperties of solids formed in stream 34. Such physical properties arepreferably determined using analyzer 131 as described above.

A simpler control system may be used if the selected level of turbulenceto achieve the preferred physical properties of solids is known. Any ofa number of flow meters well known in the art may be used to determinethe flowrate of the system. The velocity of stream 34 determined fromthe flowrate is compared to a selected velocity determined from theknown selected turbulence. A manual or automatic control system 130 isused to adjust the turbulence of stream 34 by modifying the pumpingand/or agitation rate to minimize the difference between the actualvelocity of stream 34 and the selected velocity of stream 34.

In an embodiment, flow monitoring system 39 is used to determine thevelocity or flowrate of stream 34 as it circulates through chamber 21.The velocity or flowrate may be used to estimate the turbulence level ofstream 34, and the pumping rate of pump 25 may be adjusted to achieveoptimum turbulence. In an embodiment, a flow monitoring system relayssignals to control system 130a/130b, which sends a signal to variablespeed motor 140 and/or agitator 172a/172b such that the velocity and/oragitation rate is adjusted to achieve a selected level of turbulentflow. In an embodiment, orifice plate 38 is used in conjunction withflow monitoring system 39.

Control system 130 may transmit signals that are digital or analog, andthe signals may be converted from analog to digital or from digital toanalog at multiple points in a control scheme. Feedback control may beemployed in which the turbulence of stream 34 is adjusted as a functionof system properties including: (1) the physical properties of thestream and/or the solids, (2) the fouling rate on cooling surface 24,(3) the determined level of secondary or spontaneous nucleation, and/or(4) a combination thereof. Feed-forward control may be employed in whichthe turbulence of the stream is adjusted using a model that anticipatesthe physical properties of solids, fouling rate, or onset of substantialsecondary or spontaneous nucleation. Such model would be determinedempirically from the particular system that it predicts. A controlleremploying proportional control, differential control, integral control,or any combination thereof may be used in control system 130.

Referring to FIG. 1, water and acetone removal and recovery preferablybegins in drying tower 60 downstream of first solidification system 20.Drying tower 60 is located downstream of system 20 so that the viscosityof effluent 12 is not increased before it enters chamber 21. Thevelocity that stream 34 must reach to achieve the selected level ofturbulent flow tends to decrease as the viscosity of stream 34decreases. The required pumping power tends to decrease both as thefluid viscosity decreases and as the necessary fluid velocity decreases.Thus, employing drying tower 60 downstream of system 20 facilitates thecreation of the selected level of turbulence in chamber 21, andgenerally reduces the required pumping power to achieve that turbulence.

Some practitioners allow acetone and water to remain in effluent 12and/or add water to effluent 12 prior to its introduction into asolidification unit. Such techniques are directed toward promotingcrystal formation, however they fail to favorably alter the shape of thesolids as in embodiments of the present invention. The mere addition ofwater will promote the formation of larger solids with an unchanged meanlength to width ratio. Thus, the tendency of the solids to fragment whensubjected to the centrifugal forces of solid-liquid separators will notbe significantly lessened.

In an embodiment of the invention, however, the water content ofeffluent 12 is maintained to facilitate the creation of a selectedturbulence level to alter the shape of formed solids.

Pump 25 is preferably located outside of the solidification zone.Generally, about 90% of any secondary nucleation that occurs typicallywill occur at the pump, however, no secondary nucleation can occurwithout supersaturation of stream 34. Therefore, locating the pumpoutside of the solidification zone may prevent a substantial amount ofsecondary nucleation from occurring. The solidification zone preferablyextends from point 35 (immediately after stream 34 enters cooling system23) to point 22.

In one embodiment of the invention, solidification chamber 21b includesa conduit loop having a portion of the conduit proximate to impeller 26characterized by a reduced diameter relative to the remainder of theconduit diameter. A solidification chamber that has a venturi tube maybe used to connect a conduit portion containing an impeller to a conduitportion of a much greater diameter. Enlarging the diameter of chamber21b may increase the residence time of stream 34 in chamber 21.

In another embodiment of the present invention, the diameter of chamber21b is substantially constant throughout the length of the chamber 21b,and the diameter is only slightly larger than the impeller diameter. Itis anticipated that crystal growth will occur relatively rapidly uponthe entrance of stream 34 into cooling system 23, and so increasing thediameter of chamber 21b is not preferable. The ease in which turbulenceis achieved tends to increase as the diameter of the solidificationchamber decreases.

In an embodiment, solidification chamber 21b includes slurry overflow27. Stream 34 is preferably circulated through chamber 21b, with therate of the feed entering the chamber through feed conduit 28controlling the rate that stream 34 exits through slurry overflow 27.Slurry overflow 27 is preferably a conduit having an underside 30 of itstop that is at an elevation slightly below the top 29 of thesolidification chamber 21b. The fluid level in overflow 27 typicallyremains about equal to the fluid level in the solidification chamber.When the fluid level of the solidification chamber exceeds the bottom ofthe slurry overflow conduit 27, an amount of fluid will flow down theslurry overflow, exiting first solidification system 20 to enter firstrecovery system 40. In an embodiment, the elevation of the underside 30of the top of slurry overflow 27 is between about 3 inches and about 12inches below the elevation of top 29.

In an embodiment, first solidification system 20 includes a finesdestruction or reduction system (see item 31). Fines system 31 directs aportion 36 of stream 34 through heating system 32 to heat portion 36 toa temperature slightly above the cloud point of stream 34. Heatingsystem 32 is preferably a shell and tube heat exchanger, although any ofa number of heating devices may be used. Steam is preferably used toheat portion 36, but numerous other heating media may be employed. Theresidence time of exchanger 32 and/or the temperature of the heatingmedium within exchanger 32 are preferably adjusted such that any finesthat are present are melted completely, while larger solids are onlyslightly melted. Melting tends to initiate at the ends of the largersolids, in a manner such that the length to width ratio of the solids isdecreased. In addition, first solids that are also fines tend to morestrongly resist fracture than larger first solids having the same lengthto width ratio. Thus melting the fines tends to reduce the presence offines. The fines tend to include a higher percentage of first solidsthan the larger solids formed in chamber 21a/21b. Therefore reducingfines tends to improve the mean length to width ratio of the formedsolids. Thus, fines system 31 improves the physical properties of thesolids by favorably modifying the shape of the larger solids in additionto reducing fines. Melting the fines also provides additional bisphenolA for the continued growth of the solids remaining in stream 34. In anembodiment, fines system 31 preferably draws portion 36 from chamber 21bnear point 22, and effluent 33 is redirected into chamber 21b throughfeed conduit 28.

The above-mentioned embodiments may be used in combination with oneanother. For instance, in an embodiment, solidification system 20includes: (a) a conduit loop and slurry overflow 27, (b) cooling system23b including a shell and tube heat exchanger to remove heat from stream34 to initiate solidification, (c) pump 25b with impeller 26 tocirculate the stream around the conduit loop, and (d) fines system 31,each as described above. In another embodiment, solidification system 20includes: (a) vessel 175, (b) coil 171 to remove heat from stream 34 toinitiate solidification, (c) agitator 172 with blade 173 to circulatethe stream over coil 171, and (d) fines system 31, each as describedabove. In another embodiment, solidification system includes (a) aconduit loop and slurry overflow 27, (b) cooling system 23 to removeheat from stream 34 to initiate solidification, (c) pump 25b withimpeller 26 to circulate the stream around the conduit loop and createand control the level of turbulence in stream 34, (d) agitator 172 tocreate and control additional turbulence within stream 34 and (e) finessystem 31, each as described above. First solidification system 20a(FIG. 2) is generally preferred over first solidification system 20b(FIG. 3). Numerous other combinations of embodiments describedpreviously and below will become apparent to those skilled in the art.

The use of fines system 31 tends to reduce the presence of fines butalso increases the duty of cooling system 23. Controlled turbulent flowserves to reduce the presence of fines. In an embodiment, the presenceof solids having a width of less than 60 microns is substantiallyeliminated by the selection of a suitable turbulence level in stream 34rather than the use of fines system 31.

Referring to FIG. 1, first recovery system 40 includes at least onesolid-liquid separator 41 to recover an "adduct solids" of bisphenol Awith phenol. In the context of this invention the word "adduct" means aphysical association of two or more molecules. Such an association canbe, for example, when a molecule of one component is either wholly orpartly locked within the crystal lattice of the other. An "adduct solid"including bisphenol A and phenol means a solid in which bisphenol A andphenol are both physically associated within a solid.

First recovery system 40 may include a centrifugal filter system, arotary vacuum filter system, or a pressure filter system. The filtersystems may be batch, continuous, or a combination thereof. In anembodiment, a combination of rotary vacuum and pressure filter systemsis used for enhanced wash efficiency, followed by a centrifugal filtersystem for deliquoring.

The adduct solid preferably contains bisphenol A and about 29-31 (e.g.,29.2) weight percent phenol, and more preferably bisphenol A and phenolin equimolar amounts. The adduct solid may contain more moles of phenolthan bisphenol A due to any phenol residue remaining on the surface ofthe recovered adduct solid.

In an alternate embodiment, first recovery system 40 may include batchor continuous centrifugal filters, or rotary pressure or vacuum filters,any of the above being used singularly or in combination. Batch orcentrifugal filters may be horizontal or vertical. Continuouscentrifugal filters may be "pushers", etc. Rotary pressure or vacuumfilters may be offered by Krauss-Maffei or Bird Machine Co. Preferablyfirst recovery system 40 will include a wash system to wash crystalswith phenol.

As shown in FIG. 1C (b), a vertical centrifugal filter 300 may include aperforated basket 301 upon which the crystals in line 305 (i.e., fromthe crystallizer) are filtered from the mother liquor. Wash and motherliquor exit filter 300 via line 46(b), which is fed to column 60.

First recovery system 40 alternatively includes at least one screen bowlcentrifuge 41 (see FIG. 1C (a)). Screen bowl centrifuge 41 preferablycontains flights 180 that are adapted to direct adduct solids up beachsection 44 and into screen section 45. Liquid may be directed toward theend of centrifuge 41 opposite screen section 45, upon which it may bedirected to drying tower 60 through conduit 46. Wash system 42 may beemployed to wash the solids recovered in screen bowl centrifuge 41. Thewash preferably occurs in screen section 45 of centrifuge 41 with cleanphenol serving as the wash fluid.

The recovered adduct solids are preferably crystals with a mean crystalwidth exceeding about 180 microns, and a mean length to width ratiobelow about 5:1. The recovered cake of the crystals preferably has afree liquor content of less than 6%. The crystals may in someembodiments have a rhombic shape.

In an embodiment, the recovered adduct is directed through conduit 43from the solid-liquid separator 41 to mixing system 50, where water ismixed with the adduct solid to form an adduct solution with a meltingpoint less than 150° C. The melting point of the adduct solution ispreferably between about 60° C. and 120° C., and more preferably between60° C. and 80° C. The mixing system preferably includes vessel 51 andagitator 52. In an embodiment, the mixing system also includes a heatingsystem adapted to heat water to a temperature of about 150° C. or less.Water is preferably directed into vessel 51 from water system 59 throughconduit 53 preferably at a temperature below about 150° C., morepreferably between about 60° C. and 150° C., and more preferably stillbetween about 60° C. and about 90° C. The residence time of thematerials within vessel 51 may preferably be less than 5 minutes, andmore preferably less than 1 minute. The adduct solution is preferablymixed and continuously directed to column 70 through conduit 54.

Control system 150 may be used to regulate the rate at which the adductsolution or melt is directed to column 70. In each of the followingembodiments, control system 150 is adapted to send and receive signalsfrom flow elements 151, 152, and 153, water system 59, pump 55, andheating system 57.

Flow elements 151, 152, 153 are each adapted to sense conditions of astream including temperature, pressure, and/or flow rate. Element 151includes a flow control valve to adjust the amount of water added tovessel 51. Element 153 includes a flow control valve to adjust the rateof adduct solution leaving vessel 51. In an embodiment, elements 151 and153 each relay a signal to system 150 indicating the rate of flowthrough the given element. System 150 determines the rate of adductsolid directed into vessel 51 from the relayed signals and controls theflow control valve of element 151 to direct a specified amount of waterto vessel 51.

In an embodiment, element 152 relays a signal to system 150 indicatingthe flow properties (e.g., flowrate, temperature, pressure, composition)of the effluent of system 20 that enters centrifuge 41. System 150determines a selected amount of water to be directed into vessel 51 fromthe relayed signal and controls the flow control valve of element 151 todirect a specified amount of water to vessel 51.

In another embodiment, system 150 regulates the temperature of the wateradded through conduit 53 by sending signals to a heating systemcomprised in water system 59. The heating system of water system 59adjusts the temperature of the water to a selected temperature belowabout 150° C., and more preferably between about 60° C. and about 90° C.The signal sent from system 150 to the heating system within system 59is determined by signals received by system 150 from any of elements151, 152, or 153.

In another embodiment, system 150 controls the pumping rate of pump 55as a function of the signals received from the above-mentioned elements.

Numerous additional control schemes employing the above-mentionedelements and control system may be used.

According to an embodiment, the adduct solution is treated in anion-exchange (e.g., anionic) system 58. System 58 tends to reduce and/oreliminate the presence of species such as trace acids and chlorides inthe adduct solution that catalyze the decomposition of bisphenol A. Inan embodiment, the adduct solution is at a temperature of between about60° C. and about 65° C. as it is passed through anionic exchange system58 to remove acidic species and chlorides from the adduct solution.Conventional methods are not adapted to treat the adduct solution in themanner of the present invention to remove acidic species and chlorides.An anionic exchange resin suited for such a purpose will lose itsstability above about 65° C.

Solids that enter anion exchange system 58 will tend to plug the system.The addition of water to the adduct solid or adduct solution lowers themelt point of the resulting adduct solution allowing it to pass throughsystem 58 substantially as a melt at a temperature of less than about65° C. Anionic exchange system 58 is preferably located upstream ofcolumn 70.

In an embodiment, injection system 69 (shown in FIG. 4) is used to addheated water and/or pressurizing steam to the adduct solution prior toits entrance into column 70, thereby preferably increasing thetemperature of the adduct solution to above the temperature at which theadduct solution would flash under the pressure of column 70. The steampreferably is at a temperature between about 135° C. and about 145° C.It may be necessary to add the steam at a temperature above 160° C.Steam at higher temperatures (e.g. above about 150° C.) can be added tothe adduct solution without significant decomposition of bisphenol A ifthe number of moles of phenol is at least equal to the number of molesof bisphenol A in the adduct solution. If the number of moles ofbisphenol A present is greater than the number of moles of phenolpresent, steam at higher temperatures (e.g. above about 150° C.) can beadded to the adduct solution without significant decomposition ofbisphenol A if mixing allows the temperature of the pressurized adductsolution to rapidly reach a temperature below about 150° C. Thepressurizing steam increases the temperature of the adduct solutionand/or provides sufficient pressure to allow entrance of the adductsolution into column 70.

In an embodiment, pump 55 pressurizes the adduct solution and an eductormixer is used to direct steam from system 69 into the pressurized adductsolution. In another embodiment, the steam is saturated steam at apressure of between about 50 psia and about 155 psia.

In an embodiment, heat exchanger 56 is used to raise the temperature ofthe adduct solution to about 135° C. prior to its entrance into column70. System 69 need not be employed in combination with exchanger 56 ifit is preferred to reduce the amount of water entering column 70. Pump55 may be used to pressurize the adduct solution prior to its entranceinto column 70.

In an embodiment, vessel 51 contains adduct heating system 57 to meltthe adduct solids without the addition of water. Adduct heating system57 may include external coils or other heating devices. Adduct heatingsystem 57 is adapted to heat the adduct solids to a temperature of below150° C., and the solids are preferably heated to about 135° C. Theresulting adduct melt is directed through conduit 54 to column 70, andsteam system 69 is preferably used to inject a selected amount of heatedwater or pressuring steam into the adduct melt prior to its entranceinto column 70. In this embodiment, the total quantity of waterintroduced into column 70 is decreased, thereby reducing the amount ofprocess water that must be treated. Reducing the quantity of waterintroduced into column 70 with the adduct solution may increase theenergy that must be added to column 70 for the required removal ofphenol. In an embodiment, adduct heating system 57 is used inconjunction with the method of adding of water through conduit 53 toform an adduct solution.

Referring to FIG. 4, the pressurized adduct solution is preferably at atemperature of about 135° C. as it is fed into column 70 through controlvalve 71. Column 70 includes overhead outlet 72 near the top of thecolumn, bottoms outlet 73 near the bottom of the column, and feed inlet74 between the overhead and bottoms outlets. The adduct solutionpreferably contains a suitable amount of water to allow the removal ofphenol via steam stripping at a temperature well below 150° C. in acolumn having a pressure of at least atmospheric pressure. Somepractitioners use vacuum systems to reduce the pressure within a columnto below atmospheric pressure, thereby lowering the required columntemperature. The use of a vacuum system, however, does not allow thecolumn temperature to be reduced below 157° C. since bisphenol A wouldtend to freeze in the column. In contrast, column 70 is preferablyoperated at a pressure of at least atmospheric pressure to preventseepage of air into the process stream. It is preferred to minimize theamount of oxygen in the system to minimize the formation of colorbodies. In a preferred embodiment, column 70 is operated at the pressurewhich causes the adduct solution entering column 70 to begin boiling atabout 110° C.

At least a portion of the adduct solution preferably flashes due to thepressure drop experienced across control valve 71. In one embodiment,first distributor 75 is employed to feed the adduct solution to column70 in a direction upward and parallel to the wall of the column toprevent the adduct solution from contacting the column wall and formingsolids on the column wall. In another embodiment, the column wall isheated using heating system 89 to prevent at least some of any adductsolution that contacts the column wall from forming solids on the wall.The heating system may include coil 90 or various other heating devices.Coil 90 may be adapted to contain steam or other heating media. Coil 90may be placed along any segment of the column wall. The wall ispreferably heated to a temperature of between about 110° C. and 150° C.,and more preferably between about 130° C. and about 135° C. Firstdistributor 75 and heating system 89 may be used in conjunction witheach other. In an embodiment, heating system 89 includes coil 90 alongpart or all of the length of column 70, and steam is passed through thecoil to heat the column wall.

In an embodiment, second distributor 76 is employed to distribute fluidtoward the bottom of column 70. The lower portion 78 of column 70preferably contains trays, rings, or packing 77, and heated waterinjection system 79 may be used to inject heated water into column 70through an injection port near the bottom of the column. In anembodiment, the heated water is in the form of superheated steam. Theinjection of heated water or steam near the bottom of column 70 mayfacilitate the removal of phenol remaining in the liquid phase. In anembodiment, control system 91 may be used to monitor the temperature orphenol content of bottoms stream 81 and regulate the addition of heatedwater or steam into column 70 via system 79 as a function of thetemperature or phenol content. The bottom of column 70 is preferably ata temperature of between 100° C. and 115° C., and is more preferably ata temperature of 110° C. Some solids may be allowed to travel throughtrays, rings, or packing 77 within lower portion 78 of column 70,however in an embodiment, distribution tray 88 is employed to inhibitsolids from entering the lower portion 78 of the column. Distributiontray 88 preferably prevents a sufficient amount of solids from enteringlower portion 78 to prevent significant plugging within packing 77. Inone embodiment, packing 77 may extend from lower portion 78 up todistribution tray 88.

Bottoms stream 81 is drawn from at or near the bottom of column 70 andpreferably includes less than about 1 weight percent phenol, and morepreferably includes less than about 0.5 weight percent phenol. Bottomsstream 81 preferably includes about 80-85 weight percent bisphenol A andabout 15-20 weight percent water. If the water content in the streamrises above about 15 weight percent, two liquid phases will tend toform: an organic phase including about 80-85 weight percent bisphenol Aand about 15-20 weight percent water, and an aqueous phase includingwater and a small amount of soluble bisphenol A. Bottoms stream 81preferably includes slightly above 15 weight percent water such that anemulsion is formed and excess water is present to dissolve solids. Afirst portion 82 of bottoms stream 81 is preferably recycled back intocolumn 70, preferably at a point above tray 88 and below firstdistributor 75 to prevent the absorption of vapor that contains phenolinto stream 81. The recycled bottoms portion 82 is preferably directedtoward tray 88 through second distributor 76. The recycled bottomsportion serves to wash and dissolve at least a portion of any bisphenolA solids formed in column 70. In an embodiment, water or steam is addedto recycled bottoms portion 82 through conduit 83 to enhance thedissolution of the solids, although the addition of such water is notanticipated to be necessary. Column overhead stream 84 includes phenoland water, and is directed to drying tower 60.

Control system 160 is adapted to send and receive signals from flowelements 161, 162, 163, 164, and 165. Each of these flow elements isadapted to sense conditions of a stream including temperature, pressureand/or flowrate. Control system 160 is adapted to sense columnconditions including pressure and temperatures at a plurality of sitesalong the length of the column including at tray 88 and at a feed trayin the column. Some or all of the above-mentioned flow elementspreferably contains a flow control valve. In an embodiment, an overheadstream flows from at or near the top of the column into a partialcondenser, and a portion of the overhead stream is recycled back intothe column to maintain a selected pressure within the column. The amountof the portion recycled is preferably regulated by system 160. In anembodiment, control system 160 regulates the rate of water added tobottoms recycle stream 82 through element 161 as a function of the flowrate of bottoms recycle stream 82 through element 162. In anotherembodiment, a sample of bottoms stream 81 to determine its compositionis taken at element 163, and controller 160 regulates the amount ofbottoms stream 81 that is directed through element 162 and the amount ofwater (if any) that is directed through element 161. Numerous othercontrol schemes employing the above-mentioned elements may be used.

Drying tower 60 is adapted to separate acetone and water from bisphenol,impurities, and phenol. Overhead stream 61 includes acetone and waterand is directed to a system for acetone recovery. Bottoms stream 62contains phenol, bisphenol and impurities, and is directed to a systemto recover clean phenol to be used as a phenol wash in wash system 42.

A second portion 85 of column bottoms stream 81 is preferably directedto second solidification system 100. In an embodiment, water is added tosecond portion 85 via conduit 86 to form feed stream 87 including about45-55 weight percent water, about 45-55 weight percent bisphenol A, andless than about 1 weight percent phenol. Feed stream 87 includes anorganic phase and an aqueous phase and may contain an overall watercontent up to about 75 weight percent. The organic phase includes about80-85 weight percent bisphenol A and about 15-20 weight percent water,and the aqueous phase includes water and a small quantity of solublebisphenol A. In an embodiment, second solidification system 100 includesa crystallizer 103 that contains agitator 104. In an alternateembodiment, second solidification system 100 includes a Svensondraft-tube baffled crystallizer, or a sufficiently agitated vessel. FIG.1B (a) depicts a forced circulation crystallizer 103(a). FIG. 1B (b)depicts a draft-tube crystallizer 103(b). FIG. 1B (c) depicts a Svensondraft-tube baffled crystallizer 103(c).

In an embodiment, crystallizer 103 is operated at a pressure belowatmospheric pressure such that the boiling point of water is maintainedat a temperature ranging from about 80° C. to 120° C., and morepreferably from about 94° C. to about 98° C. It may be appreciated that,in general, as temperature increases, then purity increases but yielddeclines. As such, temperature ranges such as 90-92° C., 92-94° C.,94-96° C., and/or 96-98° C. may be employed. The absolute pressure ispreferably maintained at about 500-700 torr, and more preferably atabout 600 torr. The vacuum may be achieved by vacuum system 101, whichmay include jet ejectors or a vacuum pump. Second solidification system100 may contain cooler 102 to condense a portion of the vapor enteringcooler 102 via line 201 (and returning to crystallizer 103 via line 202)that is boiled in crystallizer 103. Solids may be deposited on the wallsof crystallizer 103 due to the boiling of the fluid within crystallizer103. In an embodiment, water is added to system 103 from water system105 to minimize the evaporative cooling required, thereby inhibitingexcessive deposits from forming on the crystallizer wall. In anembodiment, water system 105 includes a water dispersing system (e.g.,sprinkler, sprayer, distributor) to introduce water into system 103(e.g., drop water onto surface). It is believed that dispersing water inthis manner enhances the formation and/or development of solids (e.g.,crystals) in system 103.

In an embodiment, second portion 85 is directed to second solidificationsystem 100 without the addition of water through conduit 86. Watersystem 105 is preferably used to add water at a select temperaturedirectly to crystallizer 103 to maintain the temperature withincrystallizer 103 between about 80° C. and 120° C., and more preferablybetween about 90° C. and 100° C. and to maintain an overall compositionwithin crystallizer 103 that includes about 45-55 weight percent waterand about 45-55 weight percent bisphenol A. Water is heated or cooled toa selected temperature using exchanger 107. This embodiment does notrequire the use of vacuum system 101 or cooler 102, since thetemperature of crystallizer 103 is maintained through the addition ofwater at a selected temperature. Thus the entry of air into the processas a result of a vacuum system is avoided. In an embodiment, vacuumsystem 101 and cooler 102 are used in conjunction with the addition ofwater from water system 105 at a selected temperature.

In an embodiment, effluent 106 from second solidification system 100 isdirected to second recovery system 110 where the high purity bisphenol Aproduct is recovered. In an embodiment, the second recovery systemcontains at least one pusher centrifuge 111 and a wash system 112 forwashing solids recovered in centrifuge 111. Pusher centrifuge 111preferably contains more than one stage and is adapted to accept washfluid from wash system 112 at a plurality of sites. The recovered solidsare preferably washed with water. Dryer 113 accepts recovered solidsthrough conduit 122 and further reduces the water content of the solids.Dryer 113 may be a fluid bed dryer 113 B or a contact dryer 113 A (seeitems I and II in FIG. 1A). Fluid bed dryer 113B may be vibrating andmay include a perforated, conveying tray 115D. Various other dryers suchas rotating tray, batch, or inclined dryers may be used. Nitrogen gas ispreferably added to contact dryer 113 to reduce the partial pressure ofwater and facilitate its removal from the recovered solids, while steampreferably serves as the heating agent and is added to dryer 113 A usingsteam system 114. The water content of the recovered solids ispreferably reduced to below 1500 ppm. Additional drying systems may beused downstream of dryer 113 to further reduce the water content of therecovered solids. If fluid bed dryer 113B is used, then a heating fluidsuch as hot nitrogen may be introduced via line 114B into distributionplenum 115B. Moist heating fluid may exit dryer 113B via conduit 115C.

The bisphenol A product is collected in hopper 120. The recoveredbisphenol A product includes at least about 99 weight percent bisphenolA, more preferably at least about 99.7 weight percent bisphenol A, andmore preferably still at least about 99.9 weight percent bisphenol A. Ina preferred embodiment, bisphenol A in the product has only been exposedto a temperature in excess of 150° C. while phenol was in molar excessof bisphenol A. In a more preferred embodiment, the greatest processtemperature to which the bisphenol A in the product has been exposed isless than 150° C.

Plant Experiments

Experiments were conducted in a BPA plant south of Bombay, India ("theIndian plant" or "the Indian process"). As operated in 1994-95, theIndian process included a reaction zone utilizing cation exchange resinfollowed by a crystallization zone that formed adduct crystals. Theadduct crystals included a one-to-one molar ratio of phenol and BPA. Theadduct crystals were recovered from the mother liquor, redissolved inclean phenol and re-crystallized in a second, identical crystallizationzone. The re-crystallized adduct crystals were again recovered andmelted, and the phenol was removed by vaporization and steam strippingafter which the final product BPA was solidified on a drum flaker. Theprimary and secondary mother liquors were both recycled to the reactionzone after being treated and/or used in various associated functions ofthe process. Water of reaction was purged from the system after removalof small quantities of contaminating phenol. Raw material was recoveredfrom a purge stream of concentrated heavy impurities and residual BPA bytreatment in a catalytic cracking system. After such treatment polymersand uncleavable heavy impurities were purged from the system. Freshacetone and phenol were added to the system to compensate for thequantities of such materials that were consumed in the formation of BPAand/or lost as waste.

In the Indian process acetone and phenol are reacted in two sequentialreactors. The reactor effluent flows directly to the primarycrystallizer system after which the adduct crystals are separated fromthe mother liquor and are re-dissolved in cleaner phenol forrecrystallization in the secondary crystallizer system. The adductcrystals from the secondary system are separated from the cleanersecondary mother liquor and are then melted. The majority of the phenolin the adduct crystal melt is vaporized from the higher boiling BPA in awiped film evaporator leaving a BPA melt containing about 1-2% residualphenol. This residual phenol is removed in a packed tower by strippingwith superheated steam. The BPA melt is solidified on a drum flaker andimmediately bagged and stored in a warehouse.

The mother liquor from the primary system contains water, acetone,impurities and residual BPA. This mother liquor is passed throughpreheaters into a flash chamber where the water, acetone and a portionof the phenol is flashed to a vapor. This vapor is fed to a distillationcolumn for separating the water and acetone from the lower vaporpressure phenol. The bottoms stream from the flash chamber includes aconcentration of impurities and residual BPA in a phenol carrier. Fromthis stream, a small purge is taken to a catalytic decomposition zonewhere the phenol is distilled overhead and the BPA and impurities arecleaved at high temperature to form phenol and isopropenyl phenol.Phenol is recovered as raw material and recycled to the reaction zone.Uncleavable "heavies" and polymers are purged from the system as "tars."The balance of the flash pot bottoms stream is recycled to the reactionzone.

The phenol in the flash pot vapor is condensed in the drying column anda portion is eventually used as the "cleaner phenol" to redissolve theadduct crystals from the primary crystallization system, and to generatethe solution feed to the secondary crystallization zone. The balance ofthe phenol is recycled to the reaction zone. The acetone, water and asmall amount of phenol vapor are fed directly into a second distillationcolumn where the acetone is recovered as distillate, and the water and asmall amount of phenol are removed from the column bottoms. The phenolis absorbed from the water in alternating beds of absorbent resin beads.The water is sent to a bio-treatment pond and discharged to a publicwaterway. The absorbed phenol is removed from the absorber beds bywashing with a portion of the recovered acetone. These acetone andphenol streams are sent back to the drying tower to separate the acetoneand water. The balance of the acetone that was not used to wash theabsorber beds is recycled to the reactors with additional acetone toreplace the acetone used in the formation of the BPA.

The mother liquor from the secondary crystallization zone is used towash the crystals from the primary crystallization zone. This motherliquor is combined with the primary mother liquor feed to the flashchamber.

Make-up phenol to replace the phenol consumed in the formation of theBPA is mixed with the phenol distillate from the adduct crystal meltprocessed through the wiped film evaporator. This mixture is used towash the adduct crystals from the secondary crystallization zone.

The water and phenol from the stream stripping tower is condensed andfed to the drying tower.

The Indian process uses 160 cubic meters, as received volume, ofunpromoted cation exchange resin catalyst to produce 5000 metric tons/yrof BPA. The Indian plant reactors are operated in series in an upflowmode at a design feed rate of about 5 metric tons/hour with circulationthrough an external cooler at a circulation rate to feed rate ratio ofabout 5:1, thus limiting temperature rise to about 1-2 degreescentigrade. The temperature rises from about 70 to about 71-72 degreesCelsius.

The reactor feed in the Indian process contains 13-15% BPA (design is10%) and 18-20% total impurities (design is about 17%). The reactoreffluent contains about 28-29% BPA (design is about 25%) and about18-20% total impurities (design is about 17%).

The Indian plant reactor feed and effluent streams are wet at 0.8-1.0%and about 1.9 to 2.0% water, respectively.

In the Indian process the total acetone sent to the reactor zone basedon net reactor feed is around 5.5-6 percent. This acetone is split withabout 1/3 being fed to the first reactor and about 2/3 being fed to thesecond reactor (the design is almost exactly the opposite). There is anincrease of about 14 to 15% BPA across the reactors which consumes about59-65% of the acetone fed, leaving about 2-2.5% acetone in the reactoreffluent.

The reactor effluent in the Indian process is sent directly to theprimary crystallization zone. The primary crystallization zone of theIndian process includes three sequential stirred, dished-head pressurevessels, each of which contains an internal cooling coil and an external"limpit" or half-pipe jacket (i.e., a jacket having a cross-sectionalshape corresponding to at least part of a semi-circle). FIG. 2 isrepresentative of these vessels. Each vessel contains two sets ofagitator blades on a single shaft, one about midway down the shaft andthe other slightly above the bottom of the vessel. The agitator bladesare all flat, sharp edged plates set at an angle of 45 degrees.

There is no cooling of the reactor effluent prior to the firstcrystallization vessel. In the first crystallizer the process is cooledfrom about 70-71 degrees C. to about 55 degrees C., in the secondcrystallizer the process is cooled to about 45 degrees C. and the thirdreduces the process temperature to about 40 degrees C. Due to lineplugging problems caused by poor temperature control (poor tracinginstallation and poor maintenance), the process is reheated to atemperature of about 50-52 degrees to avoid the effects of cold spots onthe feed line to the solids/liquid separation unit.

In addition to the details listed above, the primary crystallizationzone of the Indian system includes two standard high speed centrifugalpumps and three recycle streams that insure that the entire crystalslurry will be repeatedly subjected to the turbulence of the sharp edgedagitators and the stresses within each of the centrifugal pumps, and toinsure that the initial crystallizer vessel is continuously flooded withcrystals from the last crystallizer vessel.

The above description of the primary crystallization zone is applicableto the secondary crystallization zone. Therefore the entire systemcontains six serially arranged crystallizers with sharp edged flat plateagitators, four centrifugal pumps, and six recycle streams all of whichseem contrary to accepted good practice for promotion of good crystalgrowth. Additionally, the stream levels and temperatures of all of theunits fluctuated frequently.

As would be expected with such a system, the adduct crystal sizedistribution was extremely small with minor axes ranging from about 6microns to about 30 microns and a mean minor axis (width) on acumulative volume basis of about 18 microns. See curve A on FIG. 7. Thex-axis of FIG. 7 depicts crystal width (in microns) and the y-axisdepicts the cumulative volume for a given sample, in cubic microns.Cumulative volume was calculated by the equation: CumulativeVolume=width×width×length. Since the density of all of the crystals in agiven sample is approximately equal, the mean width calculated on acumulative volume basis would be equal to the mean width calculated on acumulative weight basis. The curves on FIG. 7 were drawn by hand, withthe data points being collected from the Indian plant.

In the Indian system the adduct crystals from the primarycrystallization zone are recovered in a centrifugal filter followed byredissolving in phenol. This solution is then passed to the secondarycrystallization zone, which is identical to the primary crystallizationzone, where the product is recrystallized as phenol/bisphenol adductcrystals. These crystals are recovered and washed in a secondcentrifugal filter and the crystals are passed on to a melt vessel wherethey are melted at about 135-140 degrees C. The melt is pumped to awiped film evaporator where the majority of the phenol is removed atabout 180 degrees C. and around 30 to 50 mm Hg. absolute pressure. Theproduct from this unit contains 1 to 2% phenol which is removed in asubsequent tower by stripping with superheated steam.

Thermal and/or catalytic cracking (decomposition) of the BPA andimpurities begins in the wiped film evaporator and continues throughoutthe following system until solidification.

The final product melt is solidified on a drum flaker from which theflake goes directly to a bagging hopper and is bagged as the flake isgenerated.

The flaked product has an assay of about 99.7 to 99.8% BPA with about0.2 to 0.3% total impurities. The ortho para isomer of BPA is low inthis product. Phenol and reaction products of decomposition seem toconstitute the majority of the impurities and, in December, 1994,product color of 40-50 APHA was the overriding problem. "APHA" refers toa color scale promulgated by the American Public Health Association forwater. APHA color measurements were made using a Klett-Summersettcalorimeter, using filter no. 42.

The Indian product had been judged to be unacceptable as a raw materialfor production of polycarbonate resins by General Electric Plastics, amajor global producer of polycarbonate resins, even when the productcolor was 15 APHA.

The particles from the Indian plant had sizes and shapes ("habits") thatwere considered particularly poor. Prior technical experts took theposition that Indian's centrifugal transfer pumps were grinding thecrystals to small particles. These experts suggested replacing thecentrifugal pumps with some type of gentle pump designed for slurries(e.g., a diaphragm pump). Other suspected causes of crystal grindingincluded the sharp edge flat plate agitators, and the control valvescontrolling the flow of slurry. The Indian design appeared to beparticularly poorly suited for controlled crystal growth.

Pursuant to conventional wisdom, certain improvements were attempted.Diaphragm pumps were installed in the Indian plant, and a frequencyconverter was installed to reduce agitator speeds. In addition, attemptswere made to modulate the swinging levels and temperatures somewhat, andto stop or reduce the recycle flows.

Crystal samples were taken after the above improvements were made andthe system had reached steady state. These samples indicated essentiallyno change in crystal size distribution. Worse still, fouling of thecooling surfaces had increased significantly due to the reduced agitatorspeeds. The operational interval between "remelts" decreaseddramatically and production began to decrease. Clearly the "conventionalwisdom" did not work for the Indian plant.

At this point the frequency converter was used to increase the agitatorspeed above original design. The operating time between remeltsincreased, indicating a significant increase in heat transfer. Within aday the centrifuge performance had improved and production was increasedby around 20% from about 13-14 metric tons per day to 16-17 metric tonsper day. The original design capacity for the Indian plant was 15 metrictons per day.

Adduct crystals were again sampled from selected points within thecrystallizer trains. Analysis indicated that the crystal size hadincreased significantly, appearing visually to be at least 3-5 times thesize of the crystals from the original sample in which the crystalwidths had ranged from 6 to 30 microns.

After some time the agitator speeds were increased again to almost themaximum allowed by the motor power. Again heat transfer increased asevidenced by another increase in operating time between necessaryremelts, followed by another improvement in centrifuge operation.Production increased to 19-20 tons per day for a total increase of40-45% above the starting point and 27-33% above design.

At this point adduct crystals were sampled from all of the 6crystallizers and the two surge pots that receive the effluent from eachcrystallizer train, and from which the centrifuges are fed. The samplesshowed a nearly complete absence of any particles that could beconsidered as `fines`. There were no particles with widths or minor axisunder 60 microns from any of the units sampled and the cumulative weightof particles with minor axis under 80 microns totaled less than 1%. Themean width of the smallest sampling was 190 microns on a cumulativeweight basis, and the mean width of the largest sampling was 300microns. The mean widths of the other six samplings fell between thosetwo with an average mean width of between 220 and 240 microns.

The most surprising data was the major axis-to-minor axis ratio (i.e.,the length to width ratio). The average of the ratios for all sampleswas 1.8 to 2.0 indicating a drastic altering of the crystal shape toshorter, more robust crystals.

Samples of the crystal cake from the centrifuge receiving the slurryfrom the primary crystallizer train showed total phenol analysis of 29to 30%, down from 35 to 40% in the earlier samples (absolutely drycrystals should be 29.2% phenol). Samples of crystal cake from thecentrifuge receiving the slurry from the secondary crystallizer trainshowed somewhat higher phenol content of 30 to 33%. This higher contentwas surprising in that the viscosity of the primary mother liquor shouldhave been significantly higher than the viscosity of the secondarymother liquor because of the much higher content of impurities (ataround 22 to 25%) versus no more than about 1% impurities in thesecondary mother liquor.

The product color had improved considerably after some operating changesto the flash system prior to the drying tower. Primary mother liquorhaving high impurities and high color is processed through this system.The mother liquor is fed into the flash system and the overhead vapor isfed to the drying tower. This overhead was supposed to be clean phenol,acetone, and water vapor but color bodies and heavies were found to beflowing overhead also. The bottoms from the drying tower are eventuallyused as the solvent for the adduct crystals from the primary system,thereby making the solution feed to the secondary system. Thereforecolor bodies that were carried over with the flash vapor into the dryingtower would eventually end up in the secondary mother liquor andcontribute color to the product in direct proportion to the amount ofmother liquor left in the cake.

Three other sources of color bodies and impurities had been found andmitigated prior to the work with the crystallizers. One was the freshphenol as it was brought in by tank truck. It was found to have highcolor and color body precursors with a vapor pressure very close tophenol, thereby preventing separation from phenol by distillation. Acation bed was installed to react the impurity with phenol to form acompound having a low vapor pressure which would allow separation of theimpurity as a heavy by distilling off the phenol. The installation andstartup of this bed was completed prior to the crystallizer work.

The second source of color bodies was from corrosion, iron and productdecomposition that was a result of improper treatment of the steamboiler feed water, and which was resulting in about 30 ppm chlorides inthe steam used to strip the residual phenol from the BPA prior toflaking. Chlorides were concentrating in the system causing stresscracking corrosion of the stainless steel drying tower and catalyzingdecomposition of BPA at high temperatures. The decomposition productswere reacting to color body precursors and color bodies.

The third source of impurities and color bodies was found to be thecatalytic cracking system for recovering raw material value from theheavy impurities that were purged from the process. This purge was takenfrom the bottoms stream from the system mentioned earlier for flashingthe primary mother liquor prior to the drying tower. The purpose of theflash system, in addition to supplying a clean stream of vapor to thedrying tower, was to generate a stream containing concentratedimpurities from which to draw the purge to the catalytic crackingsystem. It was found that the catalytic cracking system was causingincreased losses in the form of heavies generated from polymerization ofimpurities. Color body precursors, color bodies, and impurities werebeing recycled to the system with the recovered raw material, causing anincrease in impurity concentration throughout the process andtremendously increasing the color of all of the process streams. Thisoperation was improved to reduce the recycling of impurities and colorbodies to the main process streams. This operation was even shutdowncompletely for several months, which contributed to the reduction of thecolor of the process streams prior to the crystal size distributionimprovement.

The combined effect of the improvements described above had reduced theproduct color to about 20 APHA from the earlier high of 40 to 50 APHA.

With the larger crystal size distribution and the improved shape, thedeliquoring of the cake in both the primary and secondary centrifugesimproved to the point that the cake colors were actually lower than thecolor of the phenol streams used for wash. For example, the phenol usedto wash the cake in the primary centrifuge was eventually reduced to acolor of about 20 APHA but the cake discharged from the unit had a colorof 10 APHA, and the cake discharged from the secondary centrifuge had acolor of 5 APHA even when it was washed with phenol with a color of 10to 15 APHA.

It is believed that the BPA/phenol adduct crystals generated asdescribed herein have an unprecedented combination of size and shape.These crystals form a cake with desirable deliquoring characteristicsand wash efficiencies.

An unusual characteristic of the discoveries outlined herein is that theoperational change (turbulence) that seems to have the major controllinginfluence on improving the crystal shape also has a very favorableeffect on the heat transfer and, therefore, the production capacity ofthe crystallization system. The same parameter that causes the crystalto assume a favorable shape has a favorable impact on the systemcapacity.

To change the crystal shape from long and slender to short and stubby,it seems that relatively high turbulence is required. It is believe thatthe intensity of the turbulence, however, must be short of that requiredto generate spontaneous or secondary nucleation. It is difficult topredict the exact optimum turbulence for any given system because of theeffects of boundary shapes, the characteristics of different agitatorsor pump impellers, process stream compositions and temperature, thedegree of supersaturation, the viscosity of the crystallization medium,effects of crystal density, etc. The most efficient approach appears tobe to empirically determine the relationship between the ratio of thecrystal major axis to the minor axis relative to agitation orcirculation. To make this determination, crystal size distribution dataare taken for a given set of conditions and an average of themajor-to-minor-axis-ratios is calculated for the data set. The agitatorspeed or circulation rate is then increased and the system resampledafter reaching equilibrium. These steps are repeated as long as theratio of the major-to-minor axis continues to decrease and secondaryand/or spontaneous nucleation is not encountered. Crystallizer unitcapacity will tend to increase with each increase in agitation orcirculation.

In some systems additional steps can be taken to improve the crystalsize distribution as well as to improve the shape of the crystals. Theseinclude retrofitting the flow conduits to allow the reactor effluent togo directly to the crystallization zone instead of removing the water ofreaction and residual acetone prior to crystallization. This change hasthe positive effect of reducing the viscosity, which should increaseheat transfer at lower velocities and allow optimization of turbulenceat reduced power consumption (in addition to improving crystal growthand size distribution). An additional method of maximizing crystal sizedistribution is to install a system for partial or totalreduction/destruction of fines.

Incorporation of these additional approaches will increase the crystalsize distribution, however such approaches also may have some negativeside effects. The increase in water concentration in the crystallizationzone that will be experienced if the reactor effluent is used directlyas the crystallization medium will also tend to increase the solubilityof BPA in the mother liquor and could have a deleterious effect on therecovery of BPA per process pass. The installation of a fines reductionand/or destruction system will tend to increase the overall heat load onthe crystallizer cooling system, thereby negatively impactingcrystallizer capacity.

Determination of which system or combination of systems would be optimumfor any given process will require analysis of the strengths andweaknesses of the individual system.

After the improvements detailed above were made to the Indian process,samplings of the cake from the primary centrifuge showed crystals beingproduced with a color of 10-15 APHA, total phenol content of 30 to 33%,total impurities content of 0.13 to 0.27% from mother liquor with acolor of 1500 APHA, residual bisphenol of 12 to 13% and total impuritiesconcentration of 20 to 25% (a ratio of impurities/BPA of 1.67/1 to1.92/1). The crystal quality described above was produced from themother liquor described above and the crystals came from a cake that waswashed with phenol having a color of 40 APHA (3 to 4 times the color ofthe resulting cake).

These data indicate that a small amount of impurities is within thecrystal structure itself and that a system that produces crystals thatform a cake with good characteristics can produce high purity productfrom a mother liquor with a seemingly excessively high impurityconcentration. As such, with quality crystals and a good crystalprocessing system, closed loop operation in which the "reject" BPAstream from the secondary crystallization zone is recycled 100% to theprimary crystallization zone is a viable concept. This closed loopoperation is essentially the way the Indian process ran for about 3months during a time period when the catalytic cracking system wastotally shutdown. There was no detectable increase in the system ofeither the total mass of impurities or the average concentration ofimpurities during this entire time when the purge of heavy impuritiesfrom the system was zero.

After reaching equilibrium, small quantities of impurities may or maynot be generated in the reaction zone of the process. In addition, asignificant portion of this small quantity of impurities that may beformed in the reaction zone are very likely due to reaction of some ofthe decomposition products that were generated in a different area ofthe plant. In the Indian plant, it is believed that the catalyticdecomposition section of the system was destroying raw material insteadof recovering it. In addition, it is believed that this system wascontaminating the main process with heavy impurities and color bodies(and maybe color body precursors) probably to a larger extent than anyother single source.

An effective method of decolorizing process streams in the Indian plantincluded passing the stream through a "mixed" bed of cation and anionexchange resins. The bed was not actually mixed, since the anion resinwas on bottom and the cation resin was on top. This treatment was foundto be far more effective than treatment with either the cation or anionexchange resin alone. It worked very effectively to reduce the color ofall of the process streams.

Lab reactions repeated several times indicated that maintaining contactof reaction mixtures with the catalyst after the acetone has beenreacted to a very low level can result in a rapid increase in impuritiesformation, generally at the expense of BPA. Conditions that appear toenhance this phenomenon are relatively high concentrations of BPA andcorrespondingly low impurity concentrations, which tends to indicateequilibrium forces at work. This phenomenon was observed in reactionsusing all of the tested cation exchange resin catalysts, regardless ofwhether the resin was promoted or not.

It appears that a close control of acetone concentration at the end ofthe reaction and limitation of contact of reaction products with thecatalyst after completion of the reaction may be more desirable thanpushing the reaction to zero residual acetone.

Different BPA producers seem to have set different limits for impurityand BPA concentrations for good, or acceptable, crystallizerperformance. Some producers try to hold BPA concentrations at no morethan 20% in the crystallizer feed while others, who formerly ran theconcentration at around 30%, have now reduced the limit to about 25% inthe crystallizer feed. As such, it is surprising that adduct crystalshaving the size of the ones grown in the modified Indian system could begrown from a feed liquor containing 29% BPA and 20% impurities (thesefigures are based on total stream composition).

At the Indian plant the adduct crystals that were being produced priorto the modifications exhibited a size distribution on the minor axisdimension of less than about 6 microns up to about 30 microns, with acumulative mean of about 18 microns. After the modifications the systemproduced the short stubby crystals described previously with amajor-to-minor axis ratio of 1.8 to 2.0. Of all of the 6 crystallizerunits and two following surge pots sampled, the smallest particles foundmeasured greater than 60 microns on the minor axis and the largestparticles found had a minor axis of 460 microns. The smallest cumulativeweight percent mean minor axis measured for any of the 8 units was about190 microns and the largest was about 300 microns. The average mean ofall 8 units sampled was about 240 microns. These crystals were producedfrom the feed described above containing about 29% BPA and 20% totalimpurities.

As described in the process description earlier, the purification zoneof the process consisted of two crystallization zones each containingthree sequential crystallizers and a surge pot receiver. Thecrystallizers were similar in shape to those shown in FIG. 2. The surgepot, M-203, from the first three sequential crystallizers, termed"section 200," fed the first or primary solids/liquid separation systemand the adduct crystals recovered from this zone were redissolved in"clean" phenol and then re-crystallized in the second three sequentialcrystallizers, termed "section 300."

The "section 200" units included the first crystallizer, K-115, thesecond crystallizer, K-201, the third crystallizer, K-202, and the surgepot receiver, M-203. The "section 300" units included the firstrecrystallizer, K-208, the second recrystallizer, K-301, the thirdrecrystallizer, K-302, and the surge pot receiver, M-303. Thetemperature profile in both trains starts at 55 to 60 degrees C. anddrops in each succeeding unit to 40 to 43 degrees C. in the last units.The lower temperatures generally correspond to the 200 section and thehigher temperatures correspond to the 300 section.

Intuition would tend to suggest that one would see crystal growth andincreasing size distribution as the slurry progressed through thesystems, but the samples did not support this in either the 200 sectionor the 300 section. In the first crystallizer of section 200, K-115, themean width of the crystals was around 245 microns, the mean width of thesecond crystallizer, K-201, was about 300 microns but the mean width ofthe third crystallizer, K-202, dropped back to 220 microns. The meanwidth of the sampling of the receiver pot, M-203, which had no cooling,was back up to about 245 microns (i.e., essentially the same as thefirst unit, K-115. The mean width for the sampling of the first of the300 section units, K-208, turned out to be the largest of the entire 300section at about 265 microns, with the second unit, K-301, having thesmallest at about 190 microns. The mean increased slightly to about 200microns in the third crystallizer unit, K-302, and ending at about 225microns in the receiver pot M-303 (see the following table).

    ______________________________________                                               smallest largest   cumulative                                             particle particle wt. % mean average                                          width width width major-axis-to-                                             Unit (microns) (microns) (microns) minor-axis ratio                         ______________________________________                                        K-115  >80      ˜355                                                                              ˜245                                                                            2.3                                           K-201 >80 ˜460 ˜300 1.7                                           K-202 >60 ˜310 ˜220 1.8                                           M-203 >60 ˜335 ˜245 1.9                                           K-208 >80 ˜385 ˜265 2.0                                           K-301 >60 ˜250 ˜190 2.2                                           K-302 >80 ˜320 ˜215 2.0                                           K-303 >80 ˜320 ˜225 1.9                                         ______________________________________                                    

The above data do not seem to indicate any orderly progressive crystalgrowth as the slurry progresses through either the 200 system or the 300system. The data also tend to indicate that impurity concentration inthe feed, at least up to about 20% impurities, has little or nodeleterious effect on crystal growth. These data indicate that thecrystals grown from feed containing about 20% impurities and about 29%BPA (the feed to the 200 section) tended to be somewhat larger thancrystals grown from feed having an impurity concentration in the rangeof about 1-2% and a BPA concentration of about 35% (the feed to the 300section).

The following three embodiments represent experiments conducted at theIndian plant. The Indian plant solidification system is directed toforming adduct crystals including bisphenol A and about 30 weightpercent phenol. Although the embodiments have equivalent systemcharacteristics, each embodiment is operated in a different manner asdescribed below. Embodiment A is the gentlest of the embodiments, havingthe lowest circulation rate and the greatest difference in temperature(about 15° C.) between the cooling medium and the circulated stream.Embodiment B is characterized by a greatly increased circulation rateover Embodiment A such that a level of turbulence is achieved in thecirculated stream. Embodiment B has a lower temperature difference(about 5° C.) between the cooling medium and the circulated stream thandoes embodiment A. Embodiment C has an increased level of controlledturbulence relative to embodiment B and has a lower temperaturedifference (about 3° C.) between the cooling medium and stream 34 (seeFIG. 2) than does embodiment B. Embodiment C further includes finessystem 31 to heat a portion of the circulated stream. Selected physicalproperties of the solids formed in each of these embodiments fell withinthe ranges summarized below.

    ______________________________________                                                     Embodiment                                                                            Embodiment                                                                              Embodiment                                       A B C                                                                       ______________________________________                                        Total Impurities in Cake.                                                                    unknown   0.4%-0.5% 0.1%-0.2%                                    (%)                                                                           Mean Crystal Width 18 140 240                                                 (cumulative wt % basis,                                                       microns)                                                                      Mean Length to Width Ratio 3-5 2-3 1.8-2                                      Free Liquor Content of 10%-11% 3%-6% 1%-1.5%                                  Solids Cake (%)                                                             ______________________________________                                    

The above data illustrate the significant improvement in the physicalproperties of formed solids that may be observed when controlledturbulence is employed. The optimum level of turbulence and exactphysical properties of the formed solids for a particular system aredependent upon a number of factors as mentioned above and may vary amongembodiments of the invention.

Another process that may be performed is described as follows. Theadduct crystals from the primary crystallization zone are solubilized at60 degrees by addition of water. The temperature of the mixture isbrought to about 135 degrees C. and the mixture is immediatelyintroduced into a flash chamber where most of the phenol and some of thewater are removed as vapor essentially instantaneously at 100 to 110degrees C. leaving a liquid phase consisting of water and some phenol insolution in BPA melt at 100 to 110 degrees C. The liquid phase passesdownward through a distillation column wherein remaining phenol isstripped from the liquid by steam introduced at the bottom of thecolumn.

BPA/water melt containing approximately 85% BPA and 15% water exits thebottom of the column at 100 to 110 degrees C. It is introduced to asecondary crystallization zone where the temperature is reduced to 94-98degrees C. by addition of temperature controlled water to absorb thesensible heat and heat of crystallization or by addition of excess hotwater with utilization of evaporative cooling to remove the heat (or acombination of both). Large rhombic crystals of high purity BPA may berecovered by filtration or centrifugation or the like. The crystals maybe dried of the 1 to 2 percent residual moisture to yield the finalproduct of BPA.

A collection of data relating to some of the above-mentioned systemsfollows.

    ______________________________________                                        CRYSTAL SIZE DISTRIBUTION DATA                                                ______________________________________                                                                                    Cumu-                               Crys-  Actual Actual  Cumulative lative                                       tal  Length Width  Sum of weight                                              No. L/w (L) (w) (w.sup.2)(L) (w.sup.2)(L) %                                 ______________________________________                                        K-115                                                                            #2    (4.3)  499   115    6,499,275                                                                             19,277,747                                                                            2.4%                                #1 (3.5) 432 125  6,728,417  26,006,264  3.3%                                #25 (3.6) 518 144  10,749,442  36,755,706  4.7%                               #33 (3.1) 470 154  11,098,118  47,753,935  6.1%                               #14 (2.5) 403 163.2  10,738,925  58,492,760  7.4%                             #12 (3.1) 528 173  15,765,996  74,358,751  9.4%                               #16 (2.9) 509 173  15,192,637  89,451,442  11.4%                              #18 (2.2) 384 173  11,466,179 101,017,721  12.8%                              #24 (2.2) 394 182  13,094,978 114,112,699  14.5%                              #10 (2.8) 518 182  17,171,482 131,274,180  16.7%                               #5 (2.2) 413 192  15,217,459 146,401,639  19%                                #23 (1.4) 288 202  11,705,057 158,206,697  20%                                 #7 (1.6) 317 202  12,775,463 171,082,260  22%                                #29 (2.1) 422 202  17,157,417 188,249,677  24%                                 #3 (2.2) 460 211  20,479,660 208,729,337  26%                                 #4 (2.0) 451 221  21,997,191 230,726,428  29%                                 #9 (1.3) 288 221  14,040,760 244 767 288  31%                                #15 (2.0) 432 221  21,061,140 265,728,428  34%                                #26 (1.7) 394 230  20,793,925 286,722,254  36%                                #19 (2.1) 490 230  25,990,004 312,712,359  40%                                #35 (2.5) 624 250  38,775,300 351,487,659  45%                                #22 (2.0) 499 250  31,087,780 382,675,439  49%                                #32 (1.9) 499 259  33,438,472 416,214,011  54%                                #17 (1.7) 432 259  29,013,764 445,237,776  56%                                #31 (1.5) 384 259  25,798,902 471,036,697  60%                                #13 (2.1) 538 259  36,118,462 507,155,140  64%                                #20 (1.5) 413 278  31,994,708 539,149,748  68%                                #21 (1.6) 470 288  39,016,758 578,156,705  73%                                #28 (2.3) 672 298  59,416,191 637,682,796  81%                                #11 (1.3) 394 298  34,759,488 672,442,379  85%                                #30 (1.5) 480 317  48,173,775 720,716,254  91%                                 #8 (1.5) 538 355  67,727,401 788,443,655 100%                              K-208                                                                            #5    2.5    192   76.8   1,132,462                                                                               1132462                                                                             0.1%                               #38 4.3 412.8 96.0  3,704,365  4,936,727  0.5%                                 #9 2.7 288 105.6  3,211,491  8,148,418  0.8%                                 #16 1.8 201.6 115.2  2,675,462  10,723,760  1.1%                              #18 1.9 220.8 115.2  2,930,246  13,754,106  1.4%                              #45 2.3 268.8 115.2  3,467,255  17,321,361  1.8%                              #34 3.8 480 124.8  7,476,019  24,797,380  2.6%                                #30 1.7 211.2 124.8  3,279,449  28,086,729  2.9%                              #13 1.7 211.2 124.8  3,279,448  31,376,277  3.2%                              #31 3.8 508.8 134.4  9,190,638  40,466,915  4.2%                              #43 2.1 288 134.4  5,202,248  45,769,153  4.7%                                #26 1.7 249.6 144.9  5,175,705  50,944,768  5.2%                              #22 2.3 326.4 144.0  6,768,231  57,713,099  5.9%                              #11 2.8 403.2 144.0  8,360,755  66,073,754  6.8%                               #8 1.3 192 144.0  3,981,312  70,055,156  7.2%                                #17 2.0 307.2 153.6  7,247,757  77,302,923  8%                                #40 1.9 288 153.6  6,794,773  84,097,696  8.6%                                 #4 3.1 508.8 163.2  13,451,401  97,649,197  10%                               #1 2.0 326.4 163.2  8,693,416 106,342,613  11.0%                             #27 1.7 288 172.8  8,499,634 114,942,247  11.8%                               #32 1.8 336 182.4  11,178,639 126,110,786  13%                                 #6 2.4 489.6 201.6  19,798,498 146,019,484  15%                               #7 1.4 288 201.6  11,705,056 157,724,440  16%                                #24 1.7 355.2 211.2  15,743,753 173,468,393  17.9%                            #19 2.3 489.6 211.2  21,738,724 195,407,217  20%                              #20 2.0 451.2 220.8  21,997,191 217,404,408  22.4%                             #3 2.2 480 220.8  21,410,611 238,715,019  24.6%                               #2 2.0 441.6 220.8  19,697,762 258,412,781  26.6%                            #46 2.0 489.6 240.0  28,200,960 286,713,741  29.5%                            #39 1.6 384.9 240.0  22,118,600 308,732,141  31.8%                            #10 1.9 460.8 240.0  26,442,080 335,374,211  34.5%                            #25 1.4 345.6 249.6  21,430,935 356,905,156  36.7%                            #33 1.5 364.8 249.6  22,731,099 379,632,255  39%                              #36 2.1 537.6 259.2  36,114,462 415,750,717  42.8%                            #23 1.9 489.6 259.2  32,793,600 448,644,317  46%                              #12 1.7 460.8 268.8  33,279,385 481,933,702  49.6%                            #15 1.8 470.4 268.8  33,993,018 515,926,720  53%                              #21 1.5 393.6 268.8  28,438,954 544,365,674  56%                              #28 1.9 499.2 268.8  36,068,918 580,434,492  59.7%                            #35 1.7 460.8 268.8  33,294,385 613,728,977  63%                              #37 1.7 528 307.2  49,728,331 663,457,308  68.2%                              #42 1.4 432 307.2  40,768,635 704,325,943  72.6%                              #29 1.6 499.2 316.8  50,100,730 754,426,773  77.6%                            #14 1.6 499.2 316.8  50,100,771 804,427,604  82.7%                            #41 1.9 672.0 345.6  80,263,249 884,790,753  91%                              #44 1.6 595.2 384.0  87,765,712 972,456,665 100%                            K-301                                                                            #9    3.9    259.2 67.2   1,170,406                                                                             1,170,406                                                                             0.27%                               #4 3.4 355.2 105.6  3,960,963  5,131,469  1.2%                               #19 3.0 310.8 105.6  3,432,751  8,664,210  2.0%                               #31 2.0 211.2 105.6  2,355,157  11,019,387  2.5%                              #20 2.8 316.8 115.2  4,204,265  15,213,652  3.5%                              #18 3.3 384.0 115.2  5,096,080  20,319,732  4.7%                               #3 2.1 240 115.2  3,185,049  23,404,781  5.4%                                #30 3.2 403.2 124.8  6,279,756  29,784,637  6.8%                              #40 3.4 460.8 134.4  8,323,497  38,108,234  8.8%                              #35 1.8 240 134.4  4,335,206  42,443,440  9.8%                                #32 2.6 345.6 134.4  6,241,698  48,686,137  11.2%                             #27 2.8 374.4 134.4  6,762,922  55,449,059  12.8%                             #24 1.4 192.0 134.4  3,468,155  58,917,214  13.6%                              #8 2.5 336 134.4  6,069,279  64,986,413  15%                                  #7 2.6 345.6 134.4  6,247,698  71,218,211  16.4%                              #6 1.6 211.2 134.4  3,715,981  75,044,192  17.3%                             #15 2.9 393.6 134.4  7,109,739  82,153,931  19%                               #16 2.6 374.4 144.0  7,763,458  89,917,489  20.7%                             #33 1.6 230.4 144.0  4,777,474  94,695,063  21.8%                             #39 1.5 211.2 144.0  4,379,443  99,074,406  22.8%                             #11 2.5 374.4 153.6  8,733,205  10,790,711  25%                                #2 1.4 220.8 163.2  5,730,740 113,788,451  26.2%                             #25 2.2 355.2 163.2  9,460,482 123,249,033  28.4%                             #42 3.3 537.6 163.2  14,318,468 137,467,601  31.6%                            #22 1.7 288 172.8  8,499,633 146,157,234  33.6%                               #21 2.7 460.8 172.8  13,759,415 159,926,649  36.8%                            #14 1.9 336 172.8  10,032,906 169,959,455  39.1%                              #13 1.9 326.4 172.8  9,746,252 179,705,707  41%                               #12 1.8 326.4 182.4  19,759,249 190,465,056  43.8%                            #36 1.8 326.4 182.4  10,759,249 201,424,305  46.3%                            #37 1.9 355.2 182.4  11,717,418 213,241,725  49%                              #26 1.6 307.2 192  11,324,620 224,466,246  51.6%                              #28 1.7 345.6 201.6  14,046,068 238,612,414  55%                              #29 1.2 259.2 211.2  11,461,730 250,174,144  57.5%                            #23 2.0 412.8 211.2  18,413,116 268,487,270  61.8%                            #17 1.8 384 211.2  16,950,067 285,715,759  65.7%                               #5 2.0 441.6 220.8  21,429,156  30,244,925  70.7%                            #41 1.8 403.2 230.4  21,403,433 328,648,458  75.6%                             #1 2.1 480 230.4  25,480,397 354,118,755  81%                                #34 2.2 518.4 240.0  29,759,740 383,988,695  88.3%                            #10 1.6 384 240.0  22,118,400 406,107,095  93%                                #38 1.8 460.8 249.6  28,707,914 434,715,008 100%                            K-303                                                                           #18    2.5    240   96     2,211,740                                                                             2,211,740                                                                             0.4%                               #09 2.0 211 106  2,352,937  4,464,777  0.9%                                   #22 3.8 403 106  4,493,998  9,058,775  1.8%                                   #27 2.5 259 106  2,788,202  11,946,977  2%                                    #07 1.8 230 125  3,482,259  15,429,236  3%                                    #15 2.3 307 134  5,445,452  21,074,688  4%                                    #05 1.9 269 144  5,477,984  26,652,672  5.4%                                  #12 1.6 230 144  4,769,270  31,421,952  6%                                    #08 1.4 230 163  6,115,775  37,447,727  7.6%0                                 #11 1.8 288 163  7,670,661  45,218,488  9.1%                                  #13 1.4 221 163  5,786,157  51,104,655  10%                                   #24 2.1 355 173  10,600,243  61,704,798  12%                                  #16 2.0 365 182  12,143,462  73,748,361  14.8%                                #06 1.4 250 182  8,317,440  82,155,701  17%                                   #265 2.0 374 192  13,787,136  95,952,937  19%                                 #19 2.4 480 202  19,408,429 115,461,365  23.2%                                #23 1.5 307 202  12,477,266 127,938,631  26%                                  #30 1.6 336 211  14,987,428 142,926,059  28.7%                                #28 1.6 346 211  15,433,482 158,359,441  32%                                  #02 1.7 384 221  18,721,014 177,088,455  35.6%                                #03 1.9 413 221  20,134,740 197,215,396  39.6%                                #25 1.6 355 221  17,307,187 214,422,483  43%                                  #01 3.0 720 240  41,472,000 255,994,483  51.5%                                #19 2.4 586 240  33,753,600 289,748,183  58%                                  #29 1.5 374 250  23,300,260 313,048,443  63%                                  #17 1.6 394 250  24,464,263 337,494,706  68%                                  #04 1.4 403 288  33,426,432 371,021,138  74.6%                                #10 1.8 528 288  43,794,432 414,715,470  83.4%                                #20 1.5 442 288  36,661,248 451,476,718  91%                                  #21 1.3 432 326  46,023,967 497,400,785 100%                                K-201                                                                           #      1.67   124.5 57.6     414,056                                                                               414,056                                                                             0.06%                              # 2.43 163.2 67.2    736,785  1,156,741 0.16%                                 # 3.18 336.0 105.6  3,746,756  4,763,697 0.69%                                # 1.91 201.6 105.6  2,248,114  7,111,711 1.0W.                                # 2.55 268.8 105.6  1,997,485  10,109,299 1.43%                               # 1.64 172.8 105.6  1,926,955  12,036,254 1.70%                               # 1.67 192.0 115.2  2,448,039  14,484,293 2.06%                             K-302                                                                           #3     2.4    182.4 76.8   1,075,739                                                                             1,075,739                                                                             0.2%                               #5 4.3 374.4 86.4  2,794,781  3,770,720  0.7%                                 #24 2.8 240 86.4  1,791,490  5,662,310  1.0%                                  #1 2.3 259 115.2  3,439,754  9,102,154  1.7%                                  #32 2.7 307 115.2   4,076863  13,179,027  2.4%                                #18 2.3 288 124.8  4,485,612  17,664,639  3.2%                                #23 3.3 442 134.4  7,976,779  25,641,419  4.7%                                #37 2.9 384 134.4  6,936,330  32,477,749  6.0%                                #31 2.1 307 144  6,370,099  38,947,748  7.1%                                   #2 2.4 346 144  7,156,362  46,114,210  8.4%                                  #12 1.3 202 153.6  4,756,341  50,770,451  9%                                   #8 1.9 317 163.2  8,437,727  59,308,278  10.8%                               #13 1.8 288 163.2  7,670,661  66,978,939  12.2%                               #22 1.2 355 163.2  9,460,482  76,439,421  14%                                 #39 1.9 336 172.8  10,032,906  86,472,327  15.8%                              #19 1.7 298 172.8  8,786,278  95,358,615  17.4%                               #11 1.6 269 172.8  8,026,325 103,384,940  18.9%                               #10 1.5 259 172.8  7,939,671 111,114,611  20%                                 #25 1.5 269 182.4  8,942,911 120,067,422  21.9%                               #26 2.1 384 182.4  12,775,487 132,743,109  24.3%                              #27 1.7 317 182.4  10,439,760 143,382,969  26.2%                              #28 2.2 403 182.4  13,414,367 156,797,336  28.7%                              #30 2.1 384 182.4  12,775,487 169,472,923  31%                                #33 1.5 269 182.4  8,942,911 178,415,734  32.6%                               #35 1.7 317 192  11,685,788 190,201,721  34.8%                                 #9 2.1 394 192  14,418,731 204,720,453  37.4%                                 #6 2.4 461 192  16,997,656 221,718,209  40.5%                                 #4 2.3 461 201.6  18,736,210 240,454,429  43.9%                              #17 1.4 288 201.6  11,705,057 252,159,486  46%                                #16 1.7 384 220.8  18,721,014 270,780,400  49.5%                              #29 1.5 336 220.8  18,380,787 287,261,387  52.4%                              #34 1.6 374 230.4  19,753,476 307,114,763  56%                                #35 1.5 365 240  21,024,000 328,138,763  60%                                  #15 1.4 346 240  19,929,600 348,068,463  63.6%                                #20 1.7 413 249.6  25,729,966 373,798,429  68%                                #21 2.2 566 259.2  38,026,406 411,724,935  75%                                 #7 2.0 596 297.6  52,696,627 464,421,462  84.9%                              #14 1.4 413 297.6  36,477,659 501,099,211  91.5%                              #38 1.5 461 316.8  46,266,993 547,316,214 100%                              K-201                                                                           #      1.70   326.4 115.2  4,331,667                                                                             18,915,960                                                                            2.68%                              # 1.93 259.2 134.4  4,682,022  23,497,982  3.34%                              # 3.33 480.0 144.0  9,953,270  33,451,262  4.75%                              # 1.87 268.5 144.0  5,473,736  39,115,098  5.54%                              # 2.00 288.0 144.0  5,971,968  45,097,066  6.38%                              # 1.73 249.6 144.0  5,175,705  50,272,721  7.11%                              # 2.13 307.2 144.2  6,370,099  56,642,720  8.02%                              # 1.76 288.0 163.2  7,670,661  64,313,431  9.10%                              # 2.35 384.0 163.2  10,217,448  74,441,079  10.55%                            # 1.50 259.2 172.8  7,739,670  82,270,749  11.65%                             # 2.00 345.6 172.8  10,319,460  92,600,309  13.11%                            # 2.78 480.0 172.8  14,332,723 106,933,032  15.14%                            # 1.75 336.0 192.0  12,386,304 119,319,336  16.89%                            # 1.75 336.0 192.0  12,386,304 131,705,640  18.66%                            # 1.75 336.0 192.0  12,386,304 144,091,944  20.39%                            # 1.52 307.2 201.6  12,495,394 156,477,338  22.16%                            # 1.90 384.0 201.6  15,606,743 172,184,081  24.37%                            # 1.45 307.2 211.2  13,702,791 185,786,772  26.63%                            # 2.14 451.2 211.2  20,115,974 206,012,746  29.16%                            # 1.67 384.0 230.4  20,384,317 226,327,153  32.03%                            # 1.72 480.0 278.4  37,203,148 263,430,311  37.30%                            # 1.70 489.6 288.0  40,609,381 304,134,692  43.05%                            # 1.50 432.0 288.0  35,731,708 339,971,400  48.12%                            # 1.33 384.0 288.0  31,750,496 371,721,996  52.12%                            # 1.34 451.2 336.0  50,938,625 422,760,621  59.98%                            # 1.19 480.0 403  78,033,715 500,794,350  70.9%                               # 1.33 537.6 403.2  87,397,761 588,192,091  83.3%                             # 1.21 556.8 460.5 118,219,041 706,421,138 100%                             K-202                                                                           #33    1.50   288   76.8   7,156,361                                                                             7,156,361                                                                             0.1%                               #34 2.50 192.0 76.8  1,485,446  8,751,707  1.2%                                #6 2.80 268.8 96.0  2,477,260  11,219,067  1.6%                              #12 1.67 172.8 105.6  1,926,955  13,156,022  1.9%                             #30 1.73 182.4 105.6  2,034,008  26,419,097  3.7%                             #45 2.50 288.0 115.2  3,722,059  30,241,156  4.3%                             #21 3.42 393.6 115.2  5,213,481  35,464,637  5.0%                             #35 1.54 192.0 124.8  2,990,407  38,455,044  5.6%                             #11 2.05 278.4 134.4  5,028,739  43,483,783  6.1%                              #2 1.80 259.2 144.0  5,374,771  48,758,654  6.9%                              #9 2.00 288.0 144.0  5,971,968  54,730,622  7.7%                             #32 2.40 345.6 144.0  7,156,361  61,996,983  8.7%                             #44 1.94 297.6 144.0  6,171,033  68,158,016  9.6%                              #7 2.00 307.2 153.6  7,243,038  75,411,054  10.6%                            #36 2.19 336.0 153.6  7,927,234  83,338,278  11.7%                            #43 1.94 297.6 152.6  7,021,269  90,359,457  12.7%                            #47 3.14 480.0 153.6  1,324,620 101,684,177  14.3%                             #5 1.94 316.8 163.2  8,437,727 110,111,904  15.5%                            #20 1.71 278.4 163.2  7,414,972 117,436,776  16.5%                            #28 2.10 345.6 163.2  9,204,793 126,741,669  17.8%                            #46 2.12 345.6 163.2  9,204,793 135,946,462  19.1%                            #27 2.06 355.2 172.8  10,606,215 146,452,677  20.6%                           #31 2.06 355.2 172.8  10,606,215 157,158,792  22.1%                           #19 1.84 336.0 182.4  11,178,639 168,337,431  23.6%                            #1 1.85 355.2 192.0  13,094,092 181,431,623  25.5%                            #3 1.75 336.0 192.0  12,386,304 193,717,927  27.2%                           #10 2.15 412.8 192.0  15,217,459 209,035,381  29.4%                           #14 1.80 345.1 192.0  12,740,198 221,775,484  31.1%                           #15 1.75 336.0 192.0  12,386,304 234,151,784  32.9%                           #48 1.46 280.0 192.0  10,321,920 234,172,209  32.9%                           #24 1.90 384.0 201.6  15,606,743 249,778,952  35.1%                           #25 1.71 345.6 201.6  14,046,068 263,725,020  37.1%                           #29 1.43 288.0 201.6  11,705,057 275,430,079  38.7%                           #39 1.52 307.2 201.6  12,485,394 288,015,473  40.4%                           #23 1.82 384.0 211.2  17,118,488 305,143,961  42.9%                           #41 1.45 307.2 211.2  13,702,291 318,746,752  44.8%                           #13 1.73 384.0 220.8  18,721,013 337,467,765  47.4%                           #49 1.61 355.2 220.8  17,316,937 354,784,702  49.8%                            #4 1.76 422.4 240.0  24,330,240 379,214,942  53.3%                            #8 1.60 384.0 240.0  22,118,200 401,333,342  56.4%                           #12 1.53 384.0 249.6  23,923,261 425,256,603  59.7%                           #18 1.62 422.4 259.2  28,378,791 453,635,394  63.7%                           #26 1.59 412.8 259.2  27,733,719 481,369,213  67.6%                           #22 1.74 374.4 268.8  27,051,687 509,420,900  71.5%                           #42 1.68 451.2 268.8  32,600,752 541,021,652  76%                             #50 1.36 364.8 268.8  26,358,054 567,379,206  79.7%                           #17 1.83 528.0 288.0  43,794,432 611,174,138  85.8%                           #37 1.47 422.4 288.0  35,035,465 646,209,683  90.7%                           #38 1.17 336.0 288.0  27,469,184 674,078,767  94.7%                           #40 1.31 403.2 307.2  78,050,725 712,119,492 100%                           K-203                                                                           #35    2.14   144   67.2     650,270                                                                               650,270                                                                             0.135%                             #22 2.38 182.4 76.8  1,075,738  1,726,118  0.39%                              #30 1.78 153.6 86.4  1,146,617  2,772,735  0.60%                              #32 2.50 240.0 96.0  2,211,740  5,084,475  1.06%                              #29 2.50 240.0 96.0  2,211,740  7,296,415  1.52%                              #18 1.50 144.0 96.0  1,327,104  8,623,419  1.79%                               #4 2.00 192.0 96.0  1,769,472  10,392,991  2.16%                             #27 1.82 192.0 105.6  2,141,061  12,434,052  2.61%                            #33 3.00 316.8 105.6  3,432,470  16,066,702  3.34%                            #21 2.77 345.6 124.8  5,382,733  21,449,435  4.46%                            #28 2.00 249.0 124.8  3,787,429  25,337,064  5.27%                            #11 2.57 345.6 134.4  6,242,697  31,479,761  6.57%                            #16 1.53 220.8 144.0  4,478,408  36,158,26.9  7.52%                            #5 2.06 316.8 153.6  7,474,249  43,632,419  9.08%                            #17 1.50 230.4 153.6  5,435,717  49,068,335  10.21%                           #31 1.56 240.0 153.6  5,662,310  54,730,645  11.38%                            #3 3.12 508.8 163.2  13,451,401  68,272,146  14.20%                           #6 2.47 393.6 163.2  10,483,236  78,765,382  16.38%                           #9 1.56 268.8 172.8  8,026,324  86,291,706  18.05%                           #10 1.50 259.2 172.8  7,739,670  94,431,376  19.66%                           #19 1.83 316.8 172.8  9,459,497 103,990,973  21.63%                           #23 2.33 403.2 172.8  12,039,487 116,030,460  24.14%                          #26 2.28 393.6 172.8  11,752,733 127,783,293  26.58%                          #24 2.20 422.4 192.0  15,471,353 143,354,946  29.82%                          #15 1.43 288.0 201.6  11,705,057 155,059,703  32.25%                          #25 1.95 412.8 211.2  18,413,115 173,422,728  36.08%                          #20 1.61 355.2 220.8  17,316,937 190,789,765  39.69%                          #14 1.71 393.6 230.4  20,793,925 211,683,690  44.03%                          #34 1.71 393.6 230.4  20,793,925 232,477,615  48.38%                           #7 1.70 441.6 259.2  29,668,737 262,246,352  54.55%                           #2 1.93 537.6 278.4  41,667,426 303,913,778  63.22%                           #8 1.72 480.0 278.4  37,203,148 341,117,026  70.96%                          #12 1.33 384.0 288.0  31,750,496 372,917,422  77.58%                           #1 1.51 480.8 316.8  48,173,775 421,141,394  87.60%                          #13 1.57 528.0 336.0  59,619,088 480,750,485 100.00%                        ______________________________________                                    

Lab Experiments

150 grams of an adduct solid containing approximately 30 weight percentphenol and 70 weight percent bisphenol A were charged to a 2 liter, 5neck glass pot. The glass pot included a heating mantle, a steamgenerator, a sparger, and an overhead condenser and receiver. 150 gramsof water were added to the adduct solid, and the temperature of themixture was slowly increased. The mixture was completely liquefied toform an adduct solution when its temperature reached 60° C. The heatingof the solution was continued slowly, and steam sparging was performedon the solution when its temperature approached 100° C. The condensatereceived in the overhead receiver was observed to appear milky,indicating a significant presence of phenol in the overhead receiver.Sparging was continued until the condensate collected in the overheadreceiver ceased to appear milky. A sample was taken from the solution inthe glass pot and analyzed to reveal a residual phenol content of about5 weight percent. Steam sparging was continued until a sample of thesolution in the glass pot was analyzed to reveal a residual phenolcontent of less than 1 weight percent. At this time, about 400 grams ofcondensate had been collected in the overhead receiver and the watercontent of the solution in the glass pot exceeded about 20 weightpercent.

About 200 grams of water at a temperature of about 100° C. was added tothe solution in the glass pot, and the mixture was agitated and slowlycooled. A dense cloud of crystals was observed when the temperature ofthe agitated solution reached a temperature of about 98° C. The level ofagitation was increased and a portion of the agitated solution spilledthrough a large outlet on the side of the glass pot into a vacuumfilter. Crystals were recovered in the filter and washed with water at atemperature of about 100° C. in the filter. The washed crystals werelarge, well-shaped rhombic crystals having an average length of 2 to 3millimeters and a width of 1 to 1.5 millimeters, with some crystalsbeing 4 to 5 millimeters long and about 3 millimeters wide. The crystalswere partially dried overnight in an oven at a temperature of about 100°C. and analyzed by vapor pressure chromatography. The analysis indicateda content of impurities of about 175 ppm, with non-detectable levels ofphenol and the o,p isomer of bisphenol A. A subsequent analysis of thesample by a different method yielded the following concentrations ofimpurities:

    ______________________________________                                        Impurity         Concentration (ppm)                                          ______________________________________                                        phenol           non-detectable                                                 o,p isomer of bisphenol A 61                                                  trisphenol 2  9                                                               spirobiindane 90                                                              isopropenyl phenol trimer 240                                                 unknown impurities 49                                                         Total 449                                                                   ______________________________________                                    

The trisphenol 2, spirobiindane, and isopropenylphenol trimer aresuspected of being contaminants from the Indian plant phenol which atthe time was severely back-contaminated with impurities from thecatalytic cracking system.

It is expected that incorporation of a low temperature process such asthe one described above to result in improved purity of product. Theproduct is expected to have improved performance in producing highclarity polycarbonate resins compared to BPA produced in many othersystems. It is further expected that the process described herein willnot be significantly impacted by thermal and catalytic decomposition ofthe BPA product. It is expected that the BPA product will have a muchlower rate of formation of impurities and color throughout the entireprocess. The rate of formation of impurities in the process may be solow as to increase the useful operational time of any given reactor bedbetween replacement or cleanup of the bed. The incorporation of acatalytic cracking system may become obsolete because the rate offormation of impurities may be so low that the reactor beds can absorbthe impurities formed over a one to two year period at which time thebeds may be washed with a wet phenol solution to release the heavyimpurities for purge before re-commissioning the reactor.

Further modifications and alternative embodiments of various aspects ofthe invention will be apparent to those skilled in the art in view ofthis description. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the general manner of carrying out the invention. It is to beunderstood that the forms of the invention shown and described hereinare to be taken as the presently preferred embodiments. Elements andmaterials may be substituted for those illustrated and described herein,parts and processes may be reversed, and certain features of theinvention may be utilized independently, all as would be apparent to oneskilled in the art after having the benefit of this description of theinvention. Changes may be made in the elements and compositionsdescribed herein or in the features or in the sequence of features ofthe methods described herein without departing from the spirit and scopeof the invention as described in the following claims.

I claim:
 1. A system for preparing a relatively high-purity bisphenol Aproduct from an adduct solid while inhibiting decomposition of bisphenolA, the adduct solid comprising at least about 25 weight percent phenol,the system comprising:a) a first solidification system producing abisphenol A adduct solid from a first mixture of bisphenol A and phenolduring use, the adduct solid comprising at least about 25 weight percentphenol, and the first solidification system operating at a temperaturebelow 150° C.; b) a first recovery system separating at least a portionof the adduct solid from the first mixture during use, the firstrecovery system operating at a temperature below 150° C.; c) a mixingsystem heating water to a temperature less than about 150° C. duringuse, and mixing the adduct solid with the heated water during use toform a first solution comprising bisphenol A, water, and phenol; d) aseparation column adapted to reduce the concentration of phenol in thefirst solution and produce a second solution comprising bisphenol A andless than about 1 weight percent phenol during use, the columncomprising an overhead outlet near the top of the column, a bottomsoutlet near the bottom of the column, and a feed inlet between theoverhead outlet and the bottoms outlet, and the column operating at atemperature below about 150° C. during use; e) a second solidificationsystem adapted to produce a bisphenol A product from the second solutionduring use, the second solidification system operating at a temperaturebelow about 150° C. during use; and f) a second recovery system adaptedto separate at least a portion of the bisphenol A product from thesecond solution during use, the separated portion comprising at leastabout 99 weight percent bisphenol A, the second recovery systemoperating at a temperature below about 150° C. during use.
 2. The systemof claim 1, further comprising a distribution tray located within thecolumn and a feed distributor located within the column, and wherein arecycle conduit is connected to the column to recycle at least a portionof a bottoms stream from the bottoms outlet into the column at a pointbetween the distribution tray and the feed distributor.
 3. The system ofclaim 1, further comprising a reactor producing the first mixture fromthe reaction of phenol and acetone during use.
 4. The system of claim 1,further comprising a heated water injection system injecting heatedwater into the column during use.
 5. The system of claim 1, furthercomprising a heated water injection system injecting heated water intothe column during use, and wherein the heated water is in the form ofsteam.
 6. The system of claim 1, further comprising a steam injectionsystem adapted to inject steam into the column during use, and whereinthe steam injection system comprises a steam injection port located nearthe bottom of the column.
 7. The system of claim 1, further comprising atray located in the column below a feed distributor in the column, thetray adapted to screen solids and inhibit at least a portion of solidsfrom entering a bottoms stream during use.
 8. The system of claim 1,further comprising a feed distributor within the column, and wherein thecolumn comprises packing between the feed distributor and the bottomsoutlet.
 9. The system of claim 1, further comprising a steam systeminjecting steam into a column feed stream at a location upstream of thecolumn during use.
 10. The system of claim 1, further comprising aheating system heating at least a portion of the column wall during use.11. The system of claim 1, further comprising a distributor locatedwithin the column and adapted to distribute a column feed streamsubstantially parallel to the column wall during use.
 12. The system ofclaim 1 wherein the mixing system comprises a vessel with an agitator.13. The system of claim 1 wherein the first recovery system comprises atleast one screen bowl centrifuge and a phenol wash system to wash solidsduring use.
 14. The system of claim 1 wherein the second solidificationsystem comprises a draft-tube crystallizer.
 15. The system of claim 1wherein the second solidification system comprises a draft-tubecrystallizer, and further comprising a vacuum system adapted to maintainthe draft-tube crystallizer at an absolute pressure between about 500torr and about 700 torr during use.
 16. The system of claim 1 whereinthe second solidification system comprises a draft-tube crystallizer,and further comprising a cooler adapted to maintain the temperaturewithin the draft-tube crystallizer between about 90° C. and about 100°C. during use.
 17. The system of claim 1, wherein the second recoveryunit comprises at least one pusher centrifuge and a water wash system towash solids during use.
 18. The system of claim 1, wherein the secondrecovery unit comprises at least one contact dryer and a steam systemheating the heat transfer surface of the dryer during use.
 19. Thesystem of claim 1, wherein the mixing system is adapted to heat thewater to a temperature greater than about 60° C. and less than about 90°C. during use.
 20. The system of claim 1, wherein the firstsolidification system comprises a crystallizer adapted to maintain astream at a temperature greater than about 40° C. and less than about60° C. during use.
 21. The system of claim 1, wherein the firstsolidification system comprises a crystallizer and wherein thecrystallizer comprises a conduit loop, the conduit loop comprising asolidification zone that communicates with a heat exchanger.
 22. Thesystem of claim 1, further comprising a steam injection system adaptedto inject steam into the column during use, and wherein the steaminjection system comprises a steam injection port located near thebottom of the column, and further comprising a control system adapted tomonitor the phenol concentration in a bottoms stream and adjust theamount of steam injected into the column as a function of the phenolconcentration in the bottoms stream during use.
 23. The system of claim1, further comprising a steam system adapted, during use, to injectsteam into a column feed stream at a location upstream of the column,and wherein the steam injection system is adapted to inject steam havinga pressure greater than about 50 psia and less than about 155 psiaduring use.
 24. The system of claim 1, further comprising a heatingsystem adapted to heat at least a portion of the column wall to atemperature of greater than about 110° C. and less than about 150° C.during use.
 25. The system of claim 1, further comprising a heatingsystem adapted to heat the adduct solution to a temperature of less thanabout 150° C. during use, prior to the introduction of the adductsolution into the column.
 26. The system of claim 1 wherein the mixingsystem further comprises a vessel, and wherein the heating systemcomprises a shell and tube heat exchanger located downstream of thevessel.
 27. The system of claim 1 wherein the mixing system furthercomprises coils, the coils being adapted to heat the adduct solidswithin the vessel to a temperature of less than about 150° C. duringuse.
 28. The system of claim 1 wherein the second solidification systemcomprises a draft-tube crystallizer, and further comprising a watersystem adapted to add water to the draft-tube crystallizer at a selectedtemperature during use to maintain the temperature of a stream withinthe crystallizer at a selected temperature during use.
 29. The system ofclaim 1 wherein the second solidification system comprises a draft-tubecrystallizer, and further comprising a water system adapted to add waterto the draft-tube crystallizer to maintain the composition of a streamwithin the crystallizer at 40-60 weight percent water and 40-60 weightpercent bisphenol A.
 30. A system for separating phenol from a bisphenolA adduct solid while inhibiting decomposition of bisphenol A, the adductsolid comprising at least about 25 weight percent phenol, the systemcomprising:a) a mixing system adapted to heat water to a temperatureless than about 150° C. and mix the adduct solid with the heated waterto form a first solution comprising bisphenol A, water, and phenol; b) aconduit connected to allow the first solution to flow to a separationcolumn, the separation column being adapted to receive the firstsolution from the mixer and adapted to reduce the concentration ofphenol in the first solution to produce a second solution comprisingbisphenol A and less than about 1 weight percent phenol, the columncomprising an overhead outlet near the top of the column, a bottomsoutlet near the bottom of the column, and a feed inlet between theoverhead outlet and the bottoms outlet.
 31. The system of claim 1,further comprising a control system controlling the amount of heatedwater mixed with the adduct solution during use as a function of therate of a stream comprising phenol and bisphenol A entering the firstrecovery system.
 32. The system of claim 1, further comprising a controlsystem controlling the amount of heated water mixed with the adductsolution during use as a function of the rate that the adduct solutionexits the mixing system.
 33. The system of claim 1 further comprising acontrol system controlling the amount of water during use that is addedto a bottoms recycle stream comprising bisphenol A and water, the amountof water added being controlled as a function of properties of a columnbottoms stream.
 34. A system for preparing a relatively high-puritybisphenol A product from an adduct solid while inhibiting decompositionof bisphenol A, the adduct solid comprising at least about 25 weightpercent phenol, the system comprising:a) a first solidification systemproducing a bisphenol A adduct solid from a first mixture of bisphenol Aand phenol during use, the adduct solid comprising at least about 25weight percent phenol, and the first solidification system operating ata temperature below 150° C.; b) a first recovery system separating atleast a portion of the adduct solid from the first mixture during use,the first recovery system operating at a temperature below 150° C.; c) amixing system adapted to melt the adduct solid and add water at atemperature less than about 150° C. to the melted adduct solid duringuse to form a first solution comprising bisphenol A, water, and phenol;d) a separation column adapted to reduce the concentration of phenol inthe adduct solution and produce a second solution comprising bisphenol Aand less than about 1 weight percent phenol during use, the columncomprising an overhead outlet near the top of the column, a bottomsoutlet near the bottom of the column, and a feed inlet between theoverhead outlet and the bottoms outlet, and the column operating at atemperature below about 150° C. during use; e) a second solidificationsystem adapted to produce a bisphenol A product from the second solutionduring use, the second solidification system operating at a temperaturebelow about 150° C. during use; and f) a second recovery system adaptedto separate at least a portion of the bisphenol A product from thesecond solution during use, the separated portion comprising at leastabout 99 weight percent bisphenol A, the second recovery systemoperating at a temperature below about 150° C. during use.